[Qemu-devel] Bug(?): Can't unset vnc password (v1.0)

[Reeted]

In qemu-kvm 1.0 (from ubuntu Precise) I don't seem to be able to UNSET 
the vnc password once it has been set via qemu monitor.
I can set it to "" which is empty password, but a VNC client connecting 
still asks to enter a password. It does log in if I enter the empty 
string, but I think it should not ask the password at all.
Or is there any other way to disable password authentication, different 
from setting an empty password string?
Note: I am using set_password from qemu-monitor (actually libvirt's 
qemu-monitor-command).

Thank you