Its case sensitive, you must do it like this:
bodyCssClass="mybodyclass"
menuCssClass="mymenucssclass"
not BodyCssClass or MenuCssClass
There is nothing we can do to make a css class ignored if it is rendered in the markup. Generally the page settings and page layout must use the same skin as the page for a number of reasons. We "could" make it not add the body class on those pages but I'm not sure others would agree with that. Usually the body class is just used as part of a CSS selector like:
.bodyclass div.someotherclass {}
so it should be possible to construct css rules that only affect things in the actual content without affecting the layout or settings page unless you want to.
Hope that helps,
Joe