Concurrent modification exception in com.atlassian.jira.web.tags.UserTag

javax.servlet.jsp.JspTagException: Exception: java.util.ConcurrentModificationException
	at com.atlassian.jira.web.tags.UserTag.getObject(UserTag.java:24)
	at com.atlassian.util.tags.GetObjectTag.doStartTag(GetObjectTag.java:31)
	at _jsp._decorators._insecure__jsp._jspService(_insecure__jsp.java:188)
	at com.caucho.jsp.JavaPage.service(JavaPage.java:60)
	at com.caucho.jsp.Page.pageservice(Page.java:579)
	at com.caucho.server.dispatch.PageFilterChain.doFilter(PageFilterChain.java:175)
	at com.caucho.server.webapp.DispatchFilterChain.doFilter(DispatchFilterChain.java:115)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229)
	at com.caucho.server.webapp.RequestDispatcherImpl.include(RequestDispatcherImpl.java:485)
	at com.caucho.server.webapp.RequestDispatcherImpl.include(RequestDispatcherImpl.java:350)
	at com.opensymphony.module.sitemesh.filter.PageFilter.writeDecorator(PageFilter.java:173)
	at com.opensymphony.module.sitemesh.filter.PageFilter.applyDecorator(PageFilter.java:158)
	at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:62)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:182)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.seraph.filter.LoginFilter.doFilter(LoginFilter.java:181)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:132)
	at com.atlassian.jira.web.filters.JIRAProfilingFilter.doFilter(JIRAProfilingFilter.java:16)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.jira.web.filters.ActionCleanupDelayFilter.doFilter(ActionCleanupDelayFilter.java:43)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.jira.web.filters.RequestCleanupFilter.doFilter(RequestCleanupFilter.java:50)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.johnson.filters.AbstractJohnsonFilter.doFilter(AbstractJohnsonFilter.java:72)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:298)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.core.filters.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:37)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
	at com.atlassian.jira.appconsistency.db.DatabaseCompatibilityEnforcerFilter.doFilter(DatabaseCompatibilityEnforcerFilter.java:39)