BB (RIM) :: How To Add BBM Contact Permanently?

Of the 12 contacts I have on my blackberry messenger, there is one contact who I seem to be having an issue with. The problem is that although they appear on my contact list, and I on theirs, each day we have to re-invite each other. We have both requested each other on various days to see if it made a difference, but it does not. The contact is in my address book, and has their pin entered in the contact information. PIN messaging works fine, but there seems to be a issue with that one particular contact remaining a friend past midnight each day.