I am not sure if this has been reported but when I installed LR 3.4.1 64-bit the erase on the adjustment brush wouldn't work anymore. Here's a quick way to duplicate the issue: use any photo, click on adjustment brush, enable the checkbox on 'Show selected mask overlay'; paint on the brush (doesn;t matter what type of effect); now click on erase to remove the brush strokes. Nothing happens. It wouldn;t erase the strokes. I also tried toggling the Alt key to see the minus indicator. Still nothing happens. Its infuriating!