Null Login Password and X Windows

["Pedro I. Sanchez" <pedro.i.sanchez@altavista.net>]

Hello,

I have an account in my Debian box that has no password assigned to it
(empty password field in /etc/passwd). I can login from the console (any
virtual terminal) or from a telnet session and as expected no password
is required. However, when I´m logged in as some other user under X and
I type ¨su xxxxx¨ at the xterm prompt I´m always asked for a password
and just hitting return doesn´t work. The same happens when trying to
login from GDM into X, a null password doesn´t work!

Any ideas why this null password login doesn´t work under X?

Thank you,

-- 
Pedro