Actually, it's far worse than I originally thought. I went back and rebuilt the whole thing so that I only asked to build an update from 0.80 to 0.81 but WyBuild still built me an update from ALL to 0.81 and it still selects this as the preferred update when updating from 0.80 to 0.81. So whatever I do, I'm stuck with a patch which is as big as the full installer every time. I must be missing something because I can't see the point of it at all right now.