I have a Yamaha HTR-5850 receiver that is driven by a Motorola DVR on Charter cable. Lately (within the past couple of weeks) when a commercial comes on on my high definition channels, there is no center or front sound. The only sound I get is surround and subwoofer. I have it set on Prologic surround. When the show comes back on the sound is fine. What is the problem? (I assume it has to do with the commercials not being encoded properly but I'm not sure.) How can I avoid it? Thanks for any input.