Collision problem in corona physics

Hello everyone;
I’m new in corona world and I’m trying to figure out physics in corona. So I decided to develop a labyrinth game. With accelerometer you move the ball and try to reach the endpoint.
But I think I have a bug about collisions in corona physics. When the ball reaches a corner (two wall units), the ball stays there and not moving. I guess it’s about that two wall bodies try to change the ball’s velocity and direction. So my object gets locked. How can I fix this.

sorry for my language [import]uid: 142872 topic_id: 27815 reply_id: 327815[/import]

I have a video
http://www.youtube.com/watch?v=yAYieJ8AEA4&feature=plcp [import]uid: 142872 topic_id: 27815 reply_id: 112631[/import]

I have a video
http://www.youtube.com/watch?v=yAYieJ8AEA4&feature=plcp [import]uid: 142872 topic_id: 27815 reply_id: 112632[/import]