Here's some tests which show the problem reported as bug 2686. I tried to find a way to fix it but its not simple. (Note I can only confirm that XP behaves as described).
On XP yes, but it will fail on Win9x, the API doesn't guarantee that the returned size will be identical to the allocated size. Unless you have a real app that depends on that I don't think there's much point in doing that test.
Didn't the bug report a real world app requiring that behaviour? I think the reactos regedit was working on windows but failing under wine due to this exact problem, if I recall correctly.
FWIW I don't really care, I was just looking through the bugs for reproducible ones I could have a stab at :-)
Anyone from reactos comment on this?
Jason