When I build perl for my own purposes, I turn off all threading, because otherwise you pay for threading (general slowdown and memory penalty, and huge memory penalty on actual thread usage)
Its a waste to have threading support, but never actually using it, due to its instability.

On the bright side -- perl threading now is improving, plus there are new Coverity discussions on p5p ML, that shakes down and cleans many wrong places, so our chances are improving...
:)

The good thing you can do -- suggest a patch to the perl's test suite, so it will be noticed by perl porters.