Album Art Corruption

When editing some singles tracks, the art from the first track has somehow embedded itself into all the other tracks open in MP3Tag and cannot now be edited.
So track 2 now contains the correct artwork, which can be deleted etc. but also contains the artwork for track 1 which cannot be edited. I have deleted all the tags and the image still displays but I cannot get rid of it.
Will I have to recreate all those tracks that have become corrupted with an unwanted image or can I somehow delete the unwanted image from each track by manually editing each one in turn?
Thanks in advance for any help.

Where do you see that behaviour? In some 3rd party application?
What have you set for
Tools>Options>Tags> do not show pictures from folder as cover
?