A simplistic and basic description of Pro-Logic processing of a two-channel signal goes something like this:

If there is something in the left channel input that is not in the right channel, send to the left output. If there is something in the right channel input that is not in the left channel, send to the right output. If there is something in the left and right channel inputs that is the same and is in phase, send that to the center speaker. If there is something in the left and right channel inputs that is the same and is out of phase, send that to the surround speakers. If the same signal exists in left and right, but the amplitudes are different and/or if the signals are not in phase but something other than 180º out of phase, then the signal may be sent in varying amounts to different outputs.

The processing is somewhat more sophisticated than that, but the basic ‘encoding-decoding’ for all surround sound, other than end-to-end totally discrete handling of the signals, is still based on these principles.

So what happens when, somewhere in the multi-link chain of audio signal handling, including in and out of several digital audio buffers some of which are in satellite or cable digital receiver/decoders, one channel is momentarily delayed or its phase is temporarily flopped until the problem is recognized, sometimes automatically by the piece of equipment where the problem originated, and corrected? The PL processing sees the dialog portion of the signal as being present in both L and R channels, but not in phase. If you were a PL processor, where would you send this out-of-phase dialog signal?