smbmount and passwords

[Tulipánt Gergely]

Samba 2.0.5a
smbfs 2.0.1
linux 2.0.36 (RedHat 5.2)
encrypted passwords in /etc/smbpasswd

When I try to mount a share with my correct Samba password, I get:

smb_dont_catch_keepalive: server->data_ready == NULL 
mount error: Invalid argument
Please look at smbmount's manual page for possible reasons

Then once I accidentally used my UNIX password, and it works. O?O

Why? Shouldn't it use the same authentication as smbclient?