Ligh, Menu/File/Export/Save Single Image, for current frame (choice of output formats).
EDIT: Oops sorry, you already saw that, guess I'm in a hurry to get some shut eye and just partially skim read your post.
EDIT: REading a bit more in full
I think that used to be a problem in earlier versions, thought it got fixed (I'm on 32 bit build 20160407164938).
EDIT:
I've never had that problem for some time, but only just updated to VirtualDub_Pack_38543, I'll keep my eyes open for that problem
re-appearing (used Save Single Image about a half dozen times throughout the night in previous version, no problems).