This issue drove me absolutely MAD for about 3 months. I finally figured out the problem. In the BlackBerry e-mail settings area of the e-mail account you have linked to your Facebook, make sure that you have Deleted Items set to wirelessly sync. If it's not, remove your e-mail account from your device, add it again, and ensure that the box is checked is set to wirelssly sync deleted items. If that isn't enough, try sending service books and a hard reset. I deleted the Facebook app and re-installed as well.
I'm 99% sure that this is your issue, and your fix.
Let me know.
See this thread the more detail on my situation:
Last edited by jrice8002003 : 07-05-2010 at 03:17 AM.