Malformed nicknames vulnerability

If there's a user "foouser", and someone decides to log in with a nickname of "foouser " (that is, with a 0x20 space at the end, with a cracked launcher most likely), not only that the server will allow connection of such client, but won't disconnect "foouser" either.
Also, what's more severe, "foouser " will get all permissions of "foouser", and no one could kick "foouser " because of how commands are parsed.