There have been folks that have reported getting this problem while tuned to an HD MPEG4 channel. However, there seems to be more problems when tuned to MPEG-2 channels. There seems to be even more problems when tuned to an HD MPEG-2 channel. It's not clear what is causing the problem, but it looks as if the decoding algorithms stop working properly for some reason. The only thing you can do is minimize the effects, but I don't think that there is any way to completely get away from the problem.