I think I may have found a bug in CS6, but I'd like to see what others are getting. Make the Spot Healing Brush active, then Shift + right-click, and try to change the Blend mode to Luminosity. It doesn't change, although you can change to it with the drop-down on the tool bar. When I first noticed, it wouldn't change to Lighten so I rebooted PC (2 times now) and now it seems it has switched to Luminosity.
Win7, 64 bit, CS6.

