This is most likely "normal" behaviour.
Dependent of the BES server version, there is a default setting of X days and N mails a blackberry will get from the mailbox if the user never was Activated.
For the BES 4 version, this is something like 3 Days or 200 Mails. you can adujst the setting, but not in a range larger about 1000 mails or 10 Days.
see here: KB11632-How to increase the number of email messages sent to a BlackBerry smartphone during the enterprise activation process
Now, when you clone a Mailbox to a pst, and import this in the new exchange store, you also copy BES related information which is contained in the users mailbox.
Therefore even if you kill the device, it will not be seen as new.
you should have deleted the user when it was still connected to the server using the option to remove all Blackberry related information from the users mailbox.
But even then not all your mails would have reappeared.
Also, the calendar is only synced 1 month back.
This can be overcome by unchecking the wireless calendar sync, then, syncing the calendar using usb. Afterwards turn on wireless sync for the calendar again.