That's always a good one to check.
Just today, in Revit, annotation would disappear when my cursor rolled over the steering wheel, so I turned it off, since I don't use it. Then it happened at random and frequent zoom levels. Quite counterproductive since I was comparing riser diagrams to sections. Had to turn steering wheel back on and move it to a place that didn't get rolled over much. Had to wait until the end of the day for IT to update the vid card driver as I was scrambling to meet a deadline today and didn't want to risk any possible problems with a new driver, NVidia BTW. Didn't have a chance to test it out to see if it fixed the issue, though.