This has happened to me a few times since I've had T-Mobile service (5+ years). It does drive me a little nuts because I usually attempt to change it 4 or 5 times before I get fed up with it and give up for the time being. With that said, I do see that our engineers are aware of this happening, but don't have an estimated time of when it'll be updated.
Great, thanks @tmo_amanda! It's good to know I'm not the only one, and engineers are aware of the issue. It's not a biggie, but hopefully someday it can be addressed.