We've had this happen a few times on our Android devices as well, so this is absolutely NOT just an Apple issue. This is most DEFINATELY an issue with ActiveSync in general. We opened a PSS case with Microsoft a week ago which has resulted in no solutions. We are in the process of contacting Google and they are telling us that they are aware of other customers experiencing the same issues and have determined it is up to Microsoft to fix. We're in a complete catch-22 at the moment.
In a nutshell - this sucks. Fortunately, it only occurs about once a week, but Microsoft needs to seriously fix their Exchange software and we can confirm this is NOT an Apple iOS-related issue.