After updating to Exchange 2010 SP1, we had some complaints of users’ calendar items disappearing from BlackBerry smartphones. There were a couple of other complaints of BlackBerry devices not syncing properly. The following article explains the symptoms and how to resolve this issue by creating a New-ThrottlingPolicy and assigning it to your BESAdmin account.
http://www.blackberry.com/btsc/search.do?cmd=displayKC&docType=kc&externalId=KB23949