Aha, resize or maximise+restore sorts it too (I had just tried moving the window, minimise/restore and toggling the View menu entry, none of which get rid of the offset).
I tried without DWM (using Windows 7 Basic theme, or disabling desktop composition for ImgBurn.exe); the problem still occurs.
I also may not have been clear enough in not stating that this window is messed up even before I manually re-position it; the glitch occurs when the game exits fullscreen mode, not when entering it; the amount of offset also relates to the distance the window gets displaced (if it's already hard up against the right edge of the rightmost monitor when the game goes fullscreen, there's no problem).
I'm not familiar enough with Win32 programming to suggest what message might be being mis-handled, but could it be an ordering issue with messages relating to the desktop resize and redrawing? (I'm not even sure if the desktop size actually changes while the game goes fullscreen at non-native resolution, or why some games do this and some don't - whether it relates to the version of DirectX - it's more often older games which trigger this.)
I haven't noticed any similar glitches in any other application windows when this window displacement occurs, and I've seen it frequently over the past year, with a fresh Windows re-install in between.
This is ImgBurn 2.5.8.0 of course (no idea why I have menu items that Adrianvdh doesn't...).