Unfortunately I was not able to manually reproduce it. It however affects about 10% of our automated test suite. Where it appears is random, so my feeling is that this is a concurrency / race condition issue.

The code causing this at least is concurrency related.
lock(conversation);
setRequestAttribute(getRequest(), CURRENT_CONVERSATION_ATTRIBUTE_NAME, conversation);

here the return value of lock() is not checked, which may have to do with the issue.

This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira