Hello Nomolo, sorry for late reply, for some reason I was not notified about a new post on the forum.
I tested it on my mac and it does not show up twice.
In the Finder window it does show up in the side bar under mounted volumes, but on the desktop it shows up only once.
Can you please run the following terminal commands and send me the output of the last two at the moment the folder is unlocked:
cd .
cd Desktop
ls -la
mount
Btw you can launch Disk Utility and it will also show you all the mounted volumes, then pick the folder you want to lock and eject the associated volumes.
Rgds
Zsolt