I use a 47" LCD TV for a monitor; as "secondary" I get black bars on the sides; as "primary" monitor I don't get the bars. But I don't get them either way when I have IE maximized on the 47" as secondary. Also I find that if I use a wallpaper that was saved then applied then I get the bars. If I add the WP straight from a dl then I don't get the bars as secondary.
Does any of this make sense; or help?