As loading the listeners is not synchronised, when JIRA is starting up and an event is generated, the following error could occur:

2007-07-11 18:24:56,127 http-8020-Processor22 ERROR [layoutmanager.web.action.CreateIssueDetails] java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:787)
at java.util.HashMap$ValueIterator.next(HashMap.java:817)
at com.atlassian.jira.event.issue.IssueEventDispatcher.dispatchEvent(IssueEventDispatcher.java:99)
at com.atlassian.jira.event.issue.IssueEventDispatcher.dispatchEvent(IssueEventDispatcher.java:88)
at com.atlassian.jira.workflow.function.event.FireIssueEventFunction.execute(FireIssueEventFunction.java:60)
at com.opensymphony.workflow.AbstractWorkflow.executeFunction(AbstractWorkflow.java:869)
at com.opensymphony.workflow.AbstractWorkflow.transitionWorkflow(AbstractWorkflow.java:1265)
at com.opensymphony.workflow.AbstractWorkflow.initialize(AbstractWorkflow.java:618)
at com.atlassian.jira.workflow.SimpleWorkflowManager.createIssue(SimpleWorkflowManager.java:189)
at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:365)
at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:313)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)