Oh, cool, thanks. I had tried pretty much every button but that one. @_@
Also, the same receiver is connected to an SD TV, and I noticed this problem occurs on the SD TV, too, even when watching SD channels. Is there any way to fix that on the SD TV? I'm pretty sure I tried pressing the * button on the SD TV remote, and that didn't do anything (hence why I didn't think to try it on my HD TV).
On SD channels there is no "format" change allowed. It's always full screen 4:3 (on TV2.) On HD channels there are options of "Normal" which cuts off the sides of the 16:9 picture to create a 4:3 picture and "Letterbox" which scales the HD down and creates 16:9 on the 4:3 screen using black bars on the top and bottom (again, on TV2.)