Missing center channel sound on HD channels?

[Shaw Guru]

A friend noticed that while watching some HD channels it will not be coming through on his receiver in 5.1 even though it says 5.1 in the guide. He has shown me where a program will be coming through on right front and rear only and no other channels have anything coming through then the next program comes through with all 5 channels working. This has caused him to be forced to watch some of his programs using the TV speaker. Anyone else notice unusual 5.1 sound issues lately?

I've been told most amps will compensate automatically and mix the feeds faking a surround sound effect but this does not work on his amp (a little older model)