Glitch in Gamertag after signing in.

It was an old bug since 1.2 Update. But this bug is very annoying. I named my Gamertag as "PhrotonXPG"...after re-opening minecraft, It was just changed back into the username that I didn't set at all.

On the screenshot, You may see "WarnBucket" that I didn't set. It was actually "PhrotonXPG"