I bought my tv back in December and I've had this problem pretty much the whole time. At first I thought it was my cable box but I've replaced it twice and it still does it. Anyway, the problem is that I'll be watching a hi-def channel, like ESPN, it will then go to commercial and one of the commercials will be a local one that is broadcast in normal 480i. When it flips to this commerical it will be all scrambled and you can't see anything. Then when it flips back to the regular hi-def signal it will be fine.
Sometimes when it has to flip to a 480i and then back to hi-def it will flash a blue screen real quick and does this like every couple seconds. The only way to stop it is to change the channel to a regular 480i channel and then back to the hi-def channel.
Another problem, which I'm not sure is related, is whenever I turn the tv on there's a black square that takes up a lot of the screen.
I know I should have someone come out and look at it but wanted to see if anybody else has experienced any of these problems. Thx