ConcurrentModificationException retrieving versions

Found this exception in the logs immediately after an upgrade:

SEVERE: METHOD: "versionsUnreleased", exception:
java.util.ConcurrentModificationException
at org.apache.commons.collections.SequencedHashMap$OrderedIterator.next(SequencedHashMap.java:757)
at java.util.AbstractCollection.toArray(AbstractCollection.java:174)
at java.util.ArrayList.<init>(ArrayList.java:136)
at com.atlassian.jira.project.version.CachingVersionStore.getAllVersions(CachingVersionStore.java:32)
at com.atlassian.jira.project.version.DefaultVersionManager.queryDatabase(DefaultVersionManager.java:739)
at com.atlassian.jira.project.version.DefaultVersionManager.getVersionsUnreleased(DefaultVersionManager.java:431)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at webwork.util.InjectionUtils$DefaultInjectionImpl.invoke(InjectionUtils.java:61)
at webwork.util.InjectionUtils.invoke(InjectionUtils.java:52)
at webwork.util.ValueStack.findValue(ValueStack.java:426)
at webwork.util.SimpleTest.test(SimpleTest.java:391)
at webwork.util.SimpleTest.test(SimpleTest.java:476)
at webwork.util.ValueStack.test(ValueStack.java:129)
at webwork.view.taglib.IfTag.doStartTag(IfTag.java:38)
at org.apache.jsp.secure.views.browser.browseproject_jsp._jspService(browseproject_jsp.java:302)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)