I just received the latest Froyo update 2 days ago. This morning, I was woke up by my phone beeping to give me a calendar reminder (MS Exchange Account). Every single one of my monthly recurring appointments has been moved from monthly to weekly. I have a LOT of recurring appointments. I have been using this phone (Samsung Fascintate) since March without any issues or problems - all of my recurring appintments have been working without problem until I received the latest update.
That's very inconvenient to have mistakes to your appointments. I can't imagine the frustrations of having to reset your calendar. I would be glad to look into this issue. Are the Calendar appointments changing on the PC or just the device? Have you tried removing the exchange account and readding it? Email >menu>accounts> remove account. Did this start after you added any application If so please remove the application and retest. Lastly please back up the device with your Gmail account and master reset the device. For master reset instructions click here.