http://bugs.winehq.org/show_bug.cgi?id=26944
--- Comment #6 from Austin English austinenglish@gmail.com 2012-08-01 13:19:25 CDT --- (In reply to comment #5)
This occurs a LOT more often when the hard disk utilisation is high (such as during partition to partition copies or when memory is being swapped out).
I'm not sure what would cause this but it certainly seems relevant.
That brings up the possibility that it's a kernel bug.