Try with the physical target camera, turn on DOF in the command panel for the camera, Set to 'use target distance' then go into interactive mode and adjust your aperture and focal length til youre happy.
It's a bug. I will forward it to the devs now.@Yanosh, thanks a lot for reporting!The workaround is to use 3ds max Bitmap instead of Corona Bitmap. (internal note: id=241504776)