[Samba] Where does the ¨Display Name" in XP come from in a Domain?

[Chris Smith]

Where does the ¨Display Name" in XP come from in a Domain? 
I have about 300 machines that are in a ldap backended Samba 3.0
domain. I regularly add users like so:

smbldap-useradd -a -m -c "First Last" -P flast

It seem that at least at first they usually get the "First Last"
portion displayed in the start menu at the top, but often as not this
ends up being the username instead. I've experimented by changing my
own displayname variable, and this seems to work sometimes, but not
consistently.

TIA,
Christopher