When I go into the native fullscreen mode of Mac OS X (using the arrows on the upper right corner) and then press F11 to enter the fullscreen mode built into Minecraft and then press F11 again and enter the fullscreen mode of Mac OS X I get something a bar on the top of the screen (see picture)
Duplicate of MC-40597 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.