Revit appears to be incompatible with custom display scaling greater than 150%. If you've got a relatively new computer you may have a display that exceeds what Revit is currently designed to support, though I've seen reports of AutoCAD having difficulty with it too, FWIW.
I've been encountering complaints from people getting bizarre graphic display behavior when attempting to use scaling between 150-200%. It seems to be happening a bit more in the Apple camp of users that are running Windows via Boot Camp. I've even heard about a few that won't work above 100% at all.
If you're in this boat then I advise taking some Dramamine, set it back to 100%, and check your video card, settings, and drivers.