Do you have balls bouncing around?
depending on where the balls hit the screen edges, one of several things will happen. the speed could be cut in half, or doubled, the direction of playback could change (maintaining current speed), or the loop could be reset. check out the pdf in the top post under the balls section for more info.
Is this consistent with what you are seeing?
edit: just looked back at the code. for whatever reason, past mat decided to hard code the speeds .5 and 1. It might be time for a bounds update.