I have the same situation. Not sure the cause. I have not tried experimenting with settings. Only thing I may have changed is displaying volume in decibels vs ten scale. I may test a few things and will let you know if anything shows up.
I'm thinking about the purchasing an Onkyo TX-SR608 receiver.
To briefly describe the setup in my living room - I have a TV at one end of the room with a projector above it which projects to the wall at the opposite end of the room. So a screen at either end of the room.
Now, I guess this is going to make it difficult for the speaker setup because front and back of the room changes depending on which direction and screen you're looking at!
So, is it possible with the TX-SR608 to invert the speaker configuration so that front becomes back and back becomes front at the flick of a switch, without having to rewire the speakers?
I hope I explained myself enough!