Yea, thats called the moonwalk glitch (as we like to call it). Normally what I do is log in on the website (Control Panel), Then hit 'Character Fixes'.
-What I usually do is log in on website and hit 'Account already logged in Fix' then I log in and if he is still doing moonwalk (not able to log in), I hit back till I get to main menu, then I log in again and it suddenly starts working.