I've encountered this problem with my girlfriend's 8520/4.6.1.290. I sent her my mom's contact via BBM and she added it to her address book. Once she realized that she has two contacts named "Mom" in her address book she tried to delete the contact I had sent her and it wouldn't let her do so. She also can't edit the entry and each time she does she gets the "Address updated externally. Changes will be lost and the viewer closed" message. Battery pulls haven't solved the issue, as mentioned above. Contact aren't sync'd with any software so everything is edited on the phone itself.