It is the fourth issue for the same problem, other issues:
 - #1106262 (AIX 5, 2005)
 - #1234 (duplicate of #1106262, 2007)
 - #9700 (AIX 6)

The initial issue was related to semaphores and fork() (msg60639). Pass pshared=1 to sem_init() gets around this issue, but introduce new issues (msg60640). In general, locks and fork don't work together: there are still such issues in Python, see for example the issue #6721.

It looks like the behaviour of the semaphore depends on the underlying file system: see msg56228.

Nobody is able to get more information, or maybe nobody wants to dig this issue. It would be better to get the real cause of the issue, and maybe report the issue to the editor of AIX. I don't have access to this AIX, and only few Python developers have access to this OS.

At least, I would like to know if Sébastien Sablé (the author of the original patch) changed his opinion about this issue since 2007 ;-)