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All my python versions are compiled from source.

Further, since the problem only occur some of the time and 
only on some of the platforms, it's natural to suspect foul play 
from the runtime environment (i.e shell, OS) and that it might 
not be a bug in python. It's not like blocking input should be a 
black art. 

I refuse to believe that this issue has never been raised 
before and subsequently solved. It's just a matter of finding 
the right mailing list archive. The alternative seems to be 
hacking the interpreter and try to narrow it down.