Power Window cannot be deleted - Color Page

Bug: a third 'ghost' power window appears on a node that has only two power windows, as indicated in the window tab. This 'ghost' window cannot be deleted or edited at all. See attached images.
This happens in two ways:
1) I created a PW and then deleted it - but the window remained effective; and
2) I copied a node with two power windows to a new clip, and a third unwanted window appeared.
This bug can create many hours' extra work as it is easy to miss - you'd have to watch each and every clip with power windows with the highlight view turned on.
Any help would be hugely appreciated!
This happens in two ways:
1) I created a PW and then deleted it - but the window remained effective; and
2) I copied a node with two power windows to a new clip, and a third unwanted window appeared.
This bug can create many hours' extra work as it is easy to miss - you'd have to watch each and every clip with power windows with the highlight view turned on.
Any help would be hugely appreciated!