So I have a simple part, formed from two edge flanges.  One of the bend lines has dissappeared in the flat pattern.  This makes it difficult to place the bend notch marks.  I did so by measuring the flat with "merge faces" unselected, and then dimensioned the notch to that spot.  (Just to clarify why it's in the pic)

SO, why has one bend line disappeared, while the rest remain visible?