iCal Bug

I've posted a thread on this subject before, but without much response...

Basically, I'm having an issue with reminders in iCal popping up several minutes to at least a half hour after the time the event is set to start. iCal is set to automatically create reminders for five minutes prior to the beginning of any new event. When the calendar is synced to iCloud and then to my iPhone, the alarms pop up fine in the phone, but still delay on my Mac. Anybody know what the deal could be?