I'm having a similar problem. I noticed my default SMS ringtone wasn't playing for certain people and it looks like the default tone was changed. I did a battery pull and it seemed to work for me. Hope it helps you as well.
I have been having similar problems. Ever since I completed a recent system update and BB messenger update, I have been hearing the message notification sound that I have assigned to BB messenger for other things. For example my 2 different email accounts and my SMS messages all have been playing the sound assigned to BB messenger. I checked and their settings have not changed, they are still showing as having different sounds assigned to them as I had set them up. I also recently had my ringer sound change without me making any changes to the set up. I run quick pull nightly and this problem continues... Any ideas?