There have been various difficult-to-reproduce problems at thread death where dying
threads are end up on various queues after they have supposedly been removed from
those queues. This tends to cause references to dead threads and deallocated memory.
There has historically been no way to tell short of crashing that you've gotten yourself
into this state.

My test case has been to run the sorting demo, and repeatedly run sorts then hit
the page-back button. It typically has to be repeated very many times to occur,
and does various things when it occurs...

The description field as copied from bug report 1185397 follows:

I'm a moron and hate bugtool.