OS X renames secondary volume on boot
The ghost mount is probably due to an application or some aspect of the system attempting to check something after the external drive is unmounted during the shutdown process (or crash). In this case, a directory (and even subfiles) may be created.

You can get rid of this directory by simply removing it as a script. The trick is to get the script to run when the new volume is mounted. There's probably a way to do this with autofs, but I'm not so familiar with its intricacies. I would instead recommend using Lingon to automatically run the script in response to the mount request.