With 2010, I ocasionally get surfaces that go invisible. When I click on where they should be, there is an outline but I can't see it. If I change the color, it still remains invisible. The only way I can seem to get it back is to keep trying to hide/unhide the surface. Eventually I do something, and it reappears. Saving the file, and re-opening doesn't help. Neither does rebooting.Neither does cycling the transparency.