Thanks Jonas. I've logged a support question at Apple.
Btw; this is the error I get for the semaphore init:
deny ipc-posix-sem /FPC26886T2888204992
I guess this is the naming you referred to. We'll have to wait if, and how, Apple replies.
Slightly off topic; I personally have a feeling that it could be related to the naming of the semaphore. It's seems logical to expect that a semaphore only operates within the context of the sandbox that it is created in, and that would mean that there has to be a discriminator somewhere for the OS to recognize which semaphore belongs to which process. What better than use the naming for that.
Hert