Did you create the account using CalDAV, as Google recommends? It could of course be a bug in Calendar.app, but I would make sure that the recommended settings are used. See here:
Indeed, as rob speculated, Google doesn't provide Exchange ActiveSync any more for new devices:
However, that doesn't seem to be the reason for the problem in question. For me nothing was synced an a new iPhone with an Exchange type Google account, and thus, there were no events to be deleted either. I switched to using CalDAV, which works fine.