I'm not sure what to advise then. I can't swear by my life that the full 0.81a build is perfectly fine, because I took a clean 1.5 build and put a full 0.81 build on it, then installed the "a" hotfix on after it - a little different than what you are doing. But it really does seem like it is a bad install or download. Let's see what anyone else says or advises.