When I first select a single file in the file-list and then move the cursor to the Tag panel the selection color of the previously selected file is the same as the alternating gray color in the file-list as it loses focus. This is confusing because it is not clearly visible which file is selected and to which file the tag editings apply to. I suggest to:
Keep the selection when the file-list loses focus,
and/or: Use an other selection color,
or: Use check-boxes instead of selection to apply tag editings to specific files. In this case, have two additional buttons: 'Check all' and 'Check none'.