The bug was noticed during QA of 2.5.1 RC1 on Mac. The problem is that semahpore set is not detached from shared file when shared file is closed. Also it was effectively hidden with missing checks of errors, returned by ISC_event_init() function.

I suppose to add minimal fix to 2.5.1 (release semaphore set correctly) and something better, including check of shred event/mutex functions to 2.5 release branch.