Comment 4 for bug 731752

Hi Tim, I fixed a nasty bug with threading, but it would only happen when there were multiple virtual folders on the same real folder. So, this won't probably apply to your case.

Do you have any more information about what is provoking the bug for you? Note that you haven't yet sent me a good backtrace. You can only get the backtrace if set vm-thread-debug to t. If not, it just recovers from the errors as best as it can.

To turn off threading when you visit folders you need to use
  (setq-default vm-summary-show-threads nil)
C-t only works inside a single folder.

Cheers,
Uday