I reported this when I found if the folds are not 90 degrees then closed corner does not extend the face correctly (reported at approx 2012 sp4).

Now I find that at 2013 sp 4,  if the sketch defining the edge flange is not rectangular the problem occurs, even though all the edges involved are at right angles.

same geometry as it should be by modifying a rectangular edge flange afterwards.

Seems like solidworks only test closed corner functionality on square boxes, square boxes with square flanges too!