shmget() allows creation of shared memory segments with key_t key values that can be used by other processes to identify them. Traditionally, under Linux the shmctl() call could be used to caused a shared memory segment to destroy itself upon the last detachment by IPC_RMID, and this would have no other impact on the operation of the shared memory segment. This behavior of IPC_RMID is documented (in the shmctl man page) and is quite useful. However, setting IPC_RMID in recent Linux kernels has the important side effect of CHANGING the key associated with the segment to 0 (aka, IPC_PRIVATE). Ideally, this side effect should be removed from the kernel, but the kernel folks seem unlikely to do this (the new behavior was mentioned in a discussion). Thus, I suggest fixing the shmctl man page to mention this strange behavior in the discussion of IPC_RMID: after "IPC_STAT will be set." add the phrase "The segment key may be changed to IPC_PRIVATE as a side effect of IPC_RMID."
Thank you for taking the time to report this bug and helping to make Ubuntu better. You reported this bug a while ago and there hasn't been any activity in it recently. We were wondering is this still an issue for you? Can you try with latest Ubuntu release? Thanks in advance.