That happens to me as well, on some of my animations, and it seems the more I try to correct it, the more out of place things get. Not sure why it happens, but like you said, it will be fine in editor with maybe a very slight out of place happening, but when played, it really messes up. Usually I have to just start out with a new animation, and try to limit the amount I rotate and move the parts. Seems the less you rotate, the better.