I had a similar issue with comcast motorola DVR's, PS3 and Sony blu-ray. This was via the RX-V473 receiver. Well, somewhat similar. Every time I shut off the TV (LG 55"-55LH40) and switched to a different input on the receiver, when I went back to the cable box, it would reset to SD resolution and I'd have to go into the DVR's "off" menu to set it back to 1080i. If I had the cable box directly wired to the TV, it was fine. The whole reason I bough the 473 was because the yamaha I had before was too old and didn't have HDMI and I didn't want to have 4 HDMI cables going to my TV and have to deal with all the stupid adjustments on the TV for each input. Mostly because I didn't want to deal with the HDMI to TV, fiber or coax for audio to the receiver.
There was a setting in the receiver that I'm now forgetting... Myabe the HDMI-Standby SYnc or Standby Through. I can't recall, but pretty sure it was one of those. After changing those (or one of those), it would go to standby and the DVR would retain it's 1080i setting, even during a power outage. I now have the xfinity dvr and it doesn't seem to matter what setting I use, it retains the resolution setting when I power things down or switch from one to another. The more I think about it, the more I think it was when I powered down the receiver. If I left the receiver on, it would switch fine, but as soon as I flipped to standby (or lost power due to power outage), it would reset the output to SD on the DVR.
For what it's worth, I use relatively cheap dynex HDMI or monoprice cables on all my devices and they now work fine (12' or less is all I have). I only ran across this thread because I was looking at the rx-v675 because of it's dialog volume/height settings that I don't have.