[Boost-users] MultiIndexSet invariant test failure

I'm running into an invariant test failure (I have BOOST_MULTI_INDEX_INVARIANT_ASSERT defined). Specifically, the trace that follows indicates that the assert fails during a MultiIndexSet "insert" operation. Additionally, I only see this happen when I'm running multi-threaded tests. I have the call to insert() wrapped by a mutex to prevent multiple threads from calling it at the same time. Has anyone else had trouble like this? Searching the users list for multi_index and invariant doesn't turn up much. I'm using the boost library version 1_32 on RHEL3. Thanks for any help.