I have an Action defined that removes a grab-bag of unwanted fields from files.
Remove fields "ENSEMBLE;LOCATION;ENCODEDBY;..."
I added PICTURE to that rule
Remove fields "ENSEMBLE;LOCATION;ENCODEDBY;...;PICTURE"
But Mp3tag fails to remove cover art images. But if I create a Remove fields action with only PICTURE, then Mp3tag successfully removes the artwork.
I also tested a much simpler multi-field Action and it also fails.
Remove fields "PICTURE;FOO"