From the first look, I would say that you have two animations "fighting" for the right to be shown. I have to understand your code first to be really sure.
Yapp - WALKING and DEFAULT are the two compettitors
You have to review your code. Since you are useing PHYSICS your avatar gets "reflected" by the obstacles, ie. he gets thrown back y few pixels, so if the right arrow is still pressed, the plattform is still "moveing" after the short stop at the wall. The stop makes "DEFAULT" visible and then the "throwback" immediatly starts "WALKING" again...