I'm not sure if this should go here or in the DVD talk subforums, so move at will [I thought i'd try here first since it has to deal with the hardware stuff.]

I have a progressive scan DVD player hooked up thru component cables to a 60" [widescreen] HDTV. Anamorphic DVD's look excellent, of course with whatever size bars are required to keep the image the OAR.
But I put in a non-anamorphic 4:3 OAR dvd, played it through the 'HD' input, and it was 'full screen', ie, it took up the whole screen space. When I went back to non-HD connection, I could tweak the zooming, and watch in 4:3, 'zoom' [fugly], 'Widescreen' [not bad] or Auto [best.]. Couldn't do that in the 'HD' component connection [which the manual says I can't]. But I could see the image, even though the source wasn't anamorphic.

Is this normal, and if so, why does it do this? I'm not necessarily complaining, I'm just curious--I did do a lot of research, but I don't understand the reasoning behind this feature [or whatever.]

HD inputs often lock into full mode. They bypass the circuitry that allows the adjustments because they're expecting the source device to handle it.

Almost all HDTV's now will NOT lock into full mode when fed a progressive scan signal but most HDTV's 2-3 years old will most likely lock into full mode. If yours does lock into full mode you are screwed unless you can get a player like the Panasonic RP91 which has the best scaler biult into the DVD player out there! I have a Pioneer HDTV that locks into full mode and was giddy when I got my RP91 because it will scale non-Anamorphic WS DVD's to the correct aspect ratio as well as 4x3 DVD's and they look outstanding. There are some Toshibas and others that will "Zoom" the picture to achieve the correct ratio but it is NOT true scaling and is not nearly as nice a picture as the scaler in the RP91. You need to grab a RP91 as soon as possible as they are getting harder to find.