Comment 21 for bug 696431

Jonathan, thank you very much for the info! Please try this plymouth-greeter.conf, it should also work. This time the start criteria is exactly the same as in plymouth-splash.conf.
Serrano, if even this doesn't fix the problem for you, looks like I'll have to get rid of Upstart completely and provide an alternative way of starting the script. Probably utilizing sysvinit scripts might work, but they're handled by Upstart, too. I'll investigate this.