Sporadic "ConcurrentModificationException" errors

java.util.ConcurrentModificationException
		at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
		at java.util.AbstractList$Itr.next(AbstractList.java:343)
		at com.opensymphony.user.UserManager.getEntities(UserManager.java:246)
		at com.opensymphony.user.UserManager.getUsers(UserManager.java:165)
		at com.atlassian.jira.user.util.DefaultUserManager.getAllUsers(DefaultUserManager.java:68)
		at sun.reflect.GeneratedMethodAccessor712.invoke(Unknown Source)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at com.atlassian.jira.ProxyAdapter$ProxiedComponentInvocationHandler.invoke(ProxyAdapter.java:167)
		at $Proxy43.getAllUsers(Unknown Source)
		at sun.reflect.GeneratedMethodAccessor712.invoke(Unknown Source)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at com.atlassian.plugin.osgi.hostcomponents.impl.DefaultComponentRegistrar$ContextClassLoaderSettingInvocationHandler.invoke(DefaultComponentRegistrar.java:129)
		at $Proxy342.getAllUsers(Unknown Source)
		at sun.reflect.GeneratedMethodAccessor712.invoke(Unknown Source)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at com.atlassian.plugin.osgi.bridge.external.HostComponentFactoryBean$DynamicServiceInvocationHandler.invoke(HostComponentFactoryBean.java:150)
		at $Proxy342.getAllUsers(Unknown Source)
		at com.atlassian.jira.user.util.UserUtilImpl.getAllUsers(UserUtilImpl.java:522)
		at sun.reflect.GeneratedMethodAccessor1625.invoke(Unknown Source)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
		at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
		at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
		at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
		at $Proxy7464.getAllUsers(Unknown Source)
		at com.atlassian.agmp.openid.users.mgmt.jira.UserServiceImpl.getAllUsernames(UserServiceImpl.java:130)
		at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
		at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
		at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
		at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
		at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
		at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
		at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
		at $Proxy7490.getAllUsernames(Unknown Source)
		at com.atlassian.agmp.integration.jira.poller.impl.UserSynchronizerImpl.process(UserSynchronizerImpl.java:57)
		at com.atlassian.agmp.integration.jira.poller.impl.UserSynchronizerImpl.process(UserSynchronizerImpl.java:41)
		at com.atlassian.agmp.integration.jira.openid.GoogleOpenIDFilter.handleAuthSuccess(GoogleOpenIDFilter.java:408)
		at com.atlassian.agmp.integration.jira.openid.GoogleOpenIDFilter.processAuthResponseFromGoogle(GoogleOpenIDFilter.java:349)
		at com.atlassian.agmp.integration.jira.openid.GoogleOpenIDFilter.doFilter(GoogleOpenIDFilter.java:205)
		at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
		at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
		at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:55)
		at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:41)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:99)
		at com.atlassian.jira.web.filters.JIRAProfilingFilter.doFilter(JIRAProfilingFilter.java:16)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.jira.web.filters.ActionCleanupDelayFilter.doFilter(ActionCleanupDelayFilter.java:59)
		at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.jira.web.filters.RequestCleanupFilter.doFilter(RequestCleanupFilter.java:53)
		at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.johnson.filters.AbstractJohnsonFilter.doFilter(AbstractJohnsonFilter.java:72)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:350)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.gzipfilter.GzipFilter.doFilterInternal(GzipFilter.java:81)
		at com.atlassian.gzipfilter.GzipFilter.doFilter(GzipFilter.java:51)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
		at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter$1.doFilter(DelegatingPluginFilter.java:66)
		at com.atlassian.studio.core.servlet.filter.FaviconInterceptor.doFilter(FaviconInterceptor.java:58)
		at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:74)
		at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:42)
		at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:55)
		at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:41)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.core.filters.cache.AbstractCachingFilter.doFilter(AbstractCachingFilter.java:33)
		at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.core.filters.encoding.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:41)
		at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at com.atlassian.jira.startup.JiraStartupChecklistFilter.doFilter(JiraStartupChecklistFilter.java:86)
		at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
		at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
		at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
		at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
		at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
		at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
		at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:567)
		at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
		at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
		at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
		at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
		at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
		at java.lang.Thread.run(Thread.java:619)