Dropping quoted users – why sometimes Oracle can’t bear to say goodbye

After messing about with various database objects with unusual usernames, I discovered a little quirk in Oracle XE.
Obviously, you can create usernames containing quotation marks simply by quoting them on creation :

CREATE USER “MR SPOCK” IDENTIFIED BY x;
CREATE USER “MILES O'BRIEN” IDENTIFIED BY x;

And you can drop them in the same way, can’t you ?

DROP USER “MR SPOCK”;

User dropped

Logical

SQL> drop user "MILES O'BRIEN"; 
drop user "MILES O'BRIEN" 
* 
ERROR at line 1: 
ORA-00604: error occurred at recursive SQL level 1 
ORA-00933: SQL command not properly ended 
ORA-06512: at line 7 

Sneak attack by the Klingons ? Sabotage by the Romulans ? Orion Syndicate after revenge ?