This is standard BES behaviour.
On your BES server, there is a section for "message pre-population" which lets you select a default level (usually something like "7 days history" or "750 messages" - can't recall exact values but you get the idea).
When a new BB device is activated on the BES, the server uses this "pre-population" value to send some history to the device. The BES will NOT attempt to send the entire contents of a mailfile over-the-air to a BB.
The general rule of thumb is that WHENEVER you take a device from a user who has had it for months, and give them a different BB, there WILL be less data on it than the old device. This is because pre-population during EA will never send months of historical data.
See:
http://www.blackberryforums.com/bes-...lackberry.html
Other things to be aware of (as mentioned in linked thread):
* 4.1.5 BES with certain handheld OSs will give users the ability to search for messages
* Ensure that the folders you want mail to show up in have been selected for redirection
* Play about with the "swap handheld" app on newer versions of BB Desktop Manager to retain more history when swapping devices than a pure EA