Ipad/Iphone calendars missing events from exchange calendar

I have an Iphone and Ipad, both using iCal. They're set up to sync with Exchange 2010 server. Somehow both devices are missing random events from the calendar. I can see them in the outlook 2010 calendar. I've already found a solution to fix this(Turn Calendar Syncing Off and On again to rebuild the calendar). What I'm looking for is a reason as to why this is occuring. Any Ideas would be greatly appreciated. I'm using the most recent IOS on both devices.(6.0.1)