I've got a RadGrid below a RadMenu, and there seems to be some wierd overlap happening. In Firefox, I get a gray box partially behind the menu, and the contents of the grid are shoved to the right of the menu. I suspect the gray box is supposed to be the Grid's div, since the box and the grid text seem to line up pretty well.
It's also broken in IE, though it appears differently. In IE the gray box is still underneath the menu, but it is almost entirely covered by the grid contents. The grid contents are below the menu, not to the right as in Firefox.
A picture of the Firefox bug:
The IE bug (note the circled area where the gray box is visible):