Hello - as far as I can see, if I understand your comment, the preview is incorrect if edge fixing is off but the result is correct once you let up on the mouse button for your edit - is that what you see? https://mcneel.myjetbrains.com/youtrack/issue/RH-55717
Yes, the result is indeed correct. The preview is bugged (which is super annoying, since I use proportional modifications to tweak designs, which is a very visual operation).