[koland]

Guess I'll have to take your word for it. There is definitely no frame on my screen, with system default or Calibre format selected. The entire tab, from above the icons down thru the tab itself is one smooth section of white. If I change to System, then change the window background to something like yellow, then the comments box is clearly visible. I am not, however, willing to change every single program on my system to a non-white background for text, just to get some sort of separation between the two in Calibre.

Perhaps you just left it off in the version I'm running, but there are notes warning not to go past this version with Windows 7, so I haven't upgraded further.