I use Mountain Lion and sync my Mac OS X Calendar with Google Calendar using a Gmail CalDAV account in the Preferences panel of the Mac OS X Calendar app.
The problem is, when creating a new event in the Calendar app WITHOUT location, the alerts are not sync'ed correctly. Sometimes they appear in Google Calendar, sometimes they don't. But they never show up in the Calendar app, even when I edit the event to change the alert.
What I've noticed, however, is that when I write anything in the location field, everything goes smoothly.
Does this happen to you too?