Distortion from dirty pro-logic signals?

I recently purchased a 950 to replace an older Rotel preamp, and so far I've been thrilled with it. As I'm now using my home theater much more, I've noticed an odd issue.

Is it possible for there to be dirty pro-logic signals on certain cable broadcasts? I was watching CSI NY today, and I noticed that there was some dialogue leakage into the rear surrounds (more than is customary with pro logic) and that the leaking rear-channel sound would frequently distort. When I switched to the CBS HD channel, the sound on the same broadcast was perfectly clear (still pro logic, but apparently a cleaner audio signal). I've listened to a number of other pro-logic broadcasts since on other channels, and I haven't noticed any steering issue. Is it possible that certain broadcasts simply have lower-quality audio signals, despite them being nominally surround sound sources? And would this affect the pro-logic steering? (Or PLII, to be exact).

Thanks!

I've run into a few poor recordings (ads on a couple of cable channels as well as a few local news broadcasts) where there is some material that sounds as if the original recording was clipped somewhat. On the ads, this material often ends up in the surrounds, whereas the local news broadcasts tend to exhibit it on all channels. As far as the case of CSI NY, you may have run into something odd happening at the cable company or the local network affiliate - something that would not affect the HD broadcast's Dolby Digital audio. It is certainly a bit odd, though.