Android tablet bottom bar bug after turning off screen

Hi all, i have a problem. If i turn off scren on my tablet during gameplay/test of my game, and then turn it on again, two buttons from the bottom bar just dissapear. Only back and home button remains. But another problem in this is, that the home button is "unpressable", if I press it nothing happens and if I long press it it behaves strangely. ...hope anyone can help me :/

//i am using JellyBean