Apparently after this update
the box of the Filter also succumbs to this new rule - thus it is possible now to take steps backs in writing of a filtering expression. However if the user will keep pressing CTRL+Z, then the history will go back as far as before focusing on the Filter's box and writing something - thus if the user had performed some operations of files, they will be needlessly reversed
And so this issue is still unresolved fully - merely alleviated and with a caveat. Maybe there could be implemented a split into two histories of taken steps: one for the Filter box and a second for the whole rest of Mp3tag?