The Association Manager display has a built-in confusion. The extensions with extant system-provided Handlers show Metadata properties as being editable, when they are in fact __not editable__, as show highlighted in this image.
Update the Association Manager to work as follows:
1. All selected extensions have no handler: profile combo box is enabled and profile property lists are shown.
2. All selected extensions have File Meta handler: profile combo box is disabled and profile for the first selected extension is shown in combo box and profile property lists.
3. All other cases: profile combo box is disabled and profile property lists are empty.
Update the Association Manager to work as follows:
1. All selected extensions have no handler: profile combo box is enabled and profile property lists are shown.
2. All selected extensions have File Meta handler: profile combo box is disabled and profile for the first selected extension is shown in combo box and profile property lists.
3. All other cases: profile combo box is disabled and profile property lists are empty.