Since you do not use "Description" it wouldn't be in the droplist to remove it. Perhaps you can create a "Description" variable, you don't have to use it for anything...but it would appear in the dialog box so you can remove it as Ozer suggests.
It is wierd that you don't have the description in the variable drop-list, I would expect it to be there...
From my experience there were some issues with these setting when the user is logged in to more than 1 vault.
Try to see if it works correctly when the user is only logged in to the 1 vault.