I was using Internet Explorer to view some of the GYC videos on USTREAM because Firefox would not allow me to play them. While viewing them, I hopped onto the forum to check recent posts and when responding to posts, this same thing happened to me. So, after the sermons were over on USTREAM, I got out of IE and went back to Firefox and did not have that problem.
It seems as if we discovered why the screen jumps but I cannot locate the topic where we initially discussed it.