I think the calculator in Windows 7 and above took a seriously backwards step in functionality - they seem to have thought that programmers don't need exponentiation nor square roots nor floating-point(!), so there is no such function in "programmer mode" and you cannot change the number base in "scientific mode". That would only be a minor annoyance, if not for the fact that switching between modes clears the accumulator!
It is a classic case of too much modality in UI design. The first time I discovered this "feature" after losing the result of a long calculation, I thought it was a bug or I'd accidentally hit the wrong key. When I found out this was by design, it elicited a loud enough "WTF!?" that caught my co-workers attentions and caused them to exclaim the same thing after showing it to them. Fortunately the calc.exe from XP runs fine on 7 and 8.
There's another "feature" which I hadn't personally run into, but would be just as incensed if I did: