Adjustment brush edits that turn off have been acknowledged as a "bug" by Adobe see http://feedback.photoshop.com/photoshop_family/topics/problem_with_adjustment_brush_tool_i n_adobe_camera_raw Someone on a Mac posted the same problem. From feedback to my post, I had thought it was just a Windows 7 problem.
Problem is more serious than my post on Oct.16. I have discovered it is more than a Preview issue. An Adjustment Brush edit that is (momentarily) not showing in ACR 7.2 or 7.3 will not be carried over to Photoshop when you update the file into PS CS6 as a Smart Object. So you made multiple Adjustment Brush edits (for example Exposure, Highlight and Clarity) only to discover that not all the edits made it to the Photoshop Smart Object.
See original Oct. 16 post to see screen shots provided by Noel Carboni that verify bug. http://forums.adobe.com/message/4792575#4792575 Includes specs of my Windows 7 x64 machine.