There's been an issue with the forms designer for some time now, when using various Windows skins or themes that affect the default border size. For example, I use WindowBlinds 6, and am a big fan of this skin: http://wincustomize.com/skins.aspx?skinid=5306&libid=1
Using this and several other skins, when switching the forms designer from code to design view, the borders of the form often adjust themselves by a pixel or two. After many switches back and forth, this gets progressively more pronounced.
It's not a "bug" per se, perhaps - but if the designer could calculate the window border and title bar sizes instead of using the Windows default (if that's indeed what it's doing), that would be wonderful. Really, really wonderful! Resizing a form isn't too bad, but when many controls are anchored to the right and/or bottom, this gets to be a nightmare.