This is a new bug since I upgraded Lightroom to V3.2 on my MacBook Pro (Retina, Mid 2012). Here's the process I've been using for years: I import raw images from the camera's SD card. I flag the ones I intend to edit. Then I pick one to edit and duplicate it. After anywhere between half a minute to 10 minutes of editing the duplicate, the image goes black. When I go back to the Grid view, the thumbnail for that photo is also black. If I select the adjacent image in the grid to edit, and then use the arrow key to get back to the black one. Then the image reappears, but with all the edits gone.