You're correct, every time you sync with CWA it will refresh your iCal calendar. Anyone who is subscribed to that calendar will by default receive alerts for every refresh. You can easily turn this off though in iCal. Below is a link the FAQ that explains how. I put some pictures in there that should make it easy to find the right button.
I hope this helps!
Yeah, I agree. Unfortunately, it would take an enormous amount of code to update the iCal event only if it had changed. It would also be a point where bugs could creep in. So, this is the way it is for now. However, we do want to add that code eventually.
Glad you thought to turn off the alerts and fix it. Let me know if you have any other questions.