Floor Grid in 3D View is an overlay, non-occludable?
It looks like the floor grid in the Active Camera or perspective 3D views is being drawn *on top* of any imported 3D models? (instead of being occluded as you would normally expect a grid painted on the floor to be). This everything-is-transparent look is hard to follow. Is there some control that affects this, other than turning the grid off outright?