Comment 2 for bug 1240376

Kubuntu 12.04 uses kdm as its login manager; kdm is responsible for stopping plymouthd before it launches X. Reassigning to kdm, since this problem has not been reported when using lightdm.

This may be related to bug #982889; it appears kdm has not implemented the corresponding changes to improve reliability of plymouth handling at boot.

You can check whether the fix for bug #982889 solves this for you by editing /etc/init/kdm.conf on your system and changing the 'start' rule to read:

start on ((filesystem
           and runlevel [!06]
           and started dbus
           and plymouth-ready)
          or runlevel PREVLEVEL=S)