I suspect you have the contents of the 'rogue' tab a few pixels outside its boundaries. Make the tab really large and check what happens when all of its contents are most definitely contained within its boundaries.
During your editing you moved the field objects in the tab so that they extended outside the table form. Thus they now show on all of the tabs. Happens all the time. You just need to rearrange the objects on the designated tab. This can be simple or complex depending...
Any object partialy inside the tab form will show on all tab layouts.
Thanks for the help! Problem solved.