That's news to me. AFAIK, they still only serve up either 1080i or 720p in most markets. 1080p is limited mostly to Blu Ray discs. Or you only referring to a box setting and not the actual resolution of the content?
Recently had issue with a new Yamaha receiver RX-730 passing 1080p video from my Xfinity Cable Box to the TV. Sometimes it worked, sometimes it didn't. When it failed I would get a message on the Sony Bravia TV that the video signal was invalid. Had trouble clearly finding the solution online so posting what worked for me to fix it, which I did actually find ideas online so not trying to take credit, just share. Tried all kinds of tests to isolate the issue which seemed to be some sort of handshake between the TV and cable box which caused the cable box to send 1080p signals to the AVR it did not like even after I set the cable box to 1080i Issue was present both with video processing and direct, and with pass thru enabled and disabled. So when I hard set the cable box to 1080i the picture came on, but as soon as you switched stuff on and off or between sources the TV seemed to tell the cable box to turn back to 1080p which it did, and I would lose the picture and get the error. What finally worked for me was installing an HDMI splitter in front of the TV (between the AVR and the TV, but I suspect it would work between the cable box and AVR too.) You only use one output of the splitter - My assumption is the splitter prevents (blocks) the TV from telling the cable box to switch back to 1080p, so everything works fine. I leave my cable box set at 1080i (you may have to find the manual for your cable box if you do not know how to do that) which everything I read says is fine for the cable box (my other cable boxes seem to be 1080i anyway, only the DVR is seems to be 1080p) I got my splitter for under $25 at monoprice.com. Great small device. Great cables there too if you need any. Other notes on my issue: Tried a Samsung 1080p TV, same issue, so ruled out the Sony TV. Tried a Samsung 720p TV, no issue - which seemed to point to the 1080p problem. Tried all different combos of settings on the AVR with no relief. Cable box would not hold the 1080i setting which seems to be know issue for the Comcast Xfinity cable box (if they fix that may not need the splitter) But clearly it was the TV that was telling the cable box to switch back to 1080p. Had no issue with my other cablebox, yamaha ARV and Samsung TV but that cable box as noted was 1080i) And so my conclusion is the 1080p from the cable box to the AVR is what was getting messed up. Found some threads about that too saying that is not uncommon. Anyway hope this helps someone.