Gotta side with MS on this one
While there's no need for a minimized window to know the mouse position, I don't consider mouse position nearly as sensitive as keyboard input. It should still be fixed though. But where to set the limit is an interesting question. Off the top of my head, I'd say that a page in a minimized window or an inactive tab has no legitimate reason to track the mouse. But I'm not completely sure about the active tab of a background window. I'm imagining some web app that involves dragging elements chosen from a pop-up window into the main one or something like that. Seems like that could have valid uses, although there may be a better way to accomplish it.