Adding new cover to file does not enable "Save Metadata" button.

Version:

3.0.2, 4.0.0-dev and earlier

Steps to reproduce:

1. Open any mp3 file,
2. Open "Media Information",
3. Right-click on cover,
4. Select "Add cover art from file",
5. Enter valid cover file.

Result: Cover is added to dialog but button "Save Metadata" is hidden and user is unable to save change.

Workaround: Add cover, start typing something in any other field. Save button will be visible.

Expected solution:

After adding cover button to save should be visible or make save button always visible.

Recording (I have disabled recording for file selection):