iCal events automatically changed my alert time.

The events I have scheduled in iCal started alerting me today. I looked in my calendar and found that all of my events had an alert scheduled for "at time of event." I never had my events alerts turned on. I checked back several months and forward several months, and the were all on, in addition to that, I found that when I changed the alert to "none," it didn't prompt me to change all future events. So, I would have to go through and change every event. Not going to happen. Any body else have this issue? Any fixes?