One of our developers with blanket privilege on a database wanted to create a regular user mapped to a login when what he mistakenly created was a user without login and now I'm unable to remove the user. `DROP USER XX` command runs forever with no result nor an error. The user doesn't own any schemas as well. How can I remove this user?  
Thank you  
Update: I found out that SIDs of the login and the user are different! I'm not sure if this is expected behaviour since it is a user without login. If not, the question would be how to map the login and the user with the same name but with different SIDs with each other?