Does AT&T offer any services that other carriers don't provide that would require AT&T to be able to bypass the lock?
Is there anything different about AT&T's update process or syncing than android phones from other carriers?
It could be related to not having to unlock the phone each time it is synced to the user's computer.
Just AT&T rom got messed up. It could be in AT&T radio stack, or how AT&T talks back when tethering, or custom AT&T apps baked into the Rom. Very simple bug.
If you have done enough coding and testing you can easily see how this type of bug slips threw. It in an area that is not heavily tested and a simple Boolean variable got screwed up and heck it could be as simple as a bracket needs to be up or down 1 line of code. Or a line was commented out during testing and forgot to be uncommented afterwards by the dev.
I know I have done it multiple times on asignments when I was coding that a simple error like what I am talking happened all because of minor line of code and normally always happen during debugging testing tracking down one bug screwing up another part by simple forgetting. Mind you it is caught in the final run threw but generally it was on a key part of the program. Quick fix. This one is in one of those areas that just would not be caught during standard testing and was missed.
Heck I would not be surprised at all if it is not already fixed and in internal testing for a role out next week.