I have this issue, too. I won't give up Faster N9, but I have learned that you don't need a full reboot to fix it--you only need to do a refresh. I generally use N9 QRefresh from N9QuickTweaks. Minimal pain, but not an ideal solution either.

I believe that the issue must be with the coding, since the clock icon still works fine on PR1.3 with all the other stuff running. Perhaps the answer is to ask that developer to take a look or consult or put together a new app or tweak to get the calendar icon working again.