Also thanks for the reply! :)

Interesting that our results differ: as said, my code stumbles over it rather frequently,  and I can't reproduce w/o ctypes activities.  But indeed, the latter might just reinforce a race condition which is present either way...  

Yes, I also observed that a print statement (or other activities) makes the problem appear less frequently -- I would also guess that it influences a potential race somewhere.

Thanks for looking into it!

Andre.