Uh the swapping from SD to HD is normal on some screens, I've had untold HD screens until I settled on an LED one, I had the HD swap blank screen on several, its a characturistic of some of the panels to swap I can only guess the engines that supply the images from SD to HD.
Now the TV images are probably no way near as good as the PS3, number of lines the images use for TV can vary from 480 upto mostly 720p if you're lucky, even sky dont use full 1080p mate, so you will notice these differences given the PS3 is probably set to use a higher HD output to the screen than sky would give you, check your sky HD res settings cause, you can set different number of lines, not that it made any real difference tbh with mine.
Also because the panel is actually 1080 lines, they try with some panels to fill in the lines that are missing with copy pixels etc, different manufacturers use different tech some involving frame manipulation etc etc, not gonna bore you anymore but trust me what you're getting could be fairly normal overall.
Also no disrespect or being snobbish, but 656 panel isnt that good overall, the 456 was just if not better than that panel, just from my experience.
Hope it alleviates your concerns a little & best way to test panel is ok on HD is play a bluray movie through the PS3 & see if you get good 1080P video, if so then dont worry about, cause sky is synonymous for crap HD video overall, I found discovery HD was best