Semaphores with key of 0

Does anyone know how a semaphore can end up with a key value of "0"?

We have a system that had over 400 semaphores with a key value of "0" at one time. After rebooting, they don't exist anymore and all existing semaphores now have normal key values.

Any ideas on what makes this happen and if there is any way to trace where these came from? :confused:

TIA