As radhaz says I believe what you are seeing is by design, I have never seen anything different. But the fact that it's only affecting existing users and you made a server change says perms to me, but we are an Exchange shop so I could be very wrong. I would be looking at what is different on the mailserver side between the old and new users. Could also be db corruption I suppose. Try re-syncing the db (on the BES as besadmin). Change the db in db config from what it is, to what it is (RIM assure me that re-syncs
).