How do you have the audio from the Bluray player. Do you have it as PCM or Bitstream. Just a shot in the dark, but I think PCM defaults to 5.1 lossless while bitstream stays 7.1.
Now I'm positive I am talking out my arse on this, it's the end of a long day and my mind is tired (and a few cold ones) but this could be a reason (but i am doubting myself, just tossing out ideas)
I do find it odd that some movies would be in 7.1 while others are at 5.1 when saying it is 5.1 for some reason I think your reciever is just outputting the core signal at 1.5 Mbps and not the lossless
But thinking about it, PCM should also be output at 7.1
Think I need another beer.