Read-only items in the metadata pane are rendered with a grey background. However, if the user navigates to a different track and the selection of tags changes, that background sticks to the table row, even if that row might now contain a different, writable tag.

To reproduce:

1. Load any album and its audio files into Picard.
2. Select a track of your choice in the album pane.
3. Find the File Path row in the metadata pane. It has a grey background because it is read-only.
4. Now select the album itself (the line with the CD icon) in the album pane.
5. File Path is no longer displayed since there is no file that represents the whole album. However, the row in the metadata pane still has a grey background, even now holds a probably writable tag like for example Comment or Genre.

The same happens with the Length row.

Expected result: The grey background should be cleared when the row is not read-only.