pkexec bash doesn't work

[James <purpleidea gmail com>]

Using latest gnome-continous (again) recently... [1]
Want to upgrade instead of downloading a fresh image [2]

So I tried to upgrade it:

pkexec bash

prompts with a GNOME shell password dialog. Entering the user
password, or empty or 'password' doesn't work.
So I can't get root to upgrade...

Does this work for anyone else?
Are the docs just out of date [3]?

Cheers,
James

[1] Especially useful to try out git master before it hits stable!
Awesome. Combined with gtk-inspector, this is wicked.
[2] I don't want to wait for another 12 hours for
https://mail.gnome.org/archives/gnome-continuous-list/2014-October/msg00018.html
[3] https://wiki.gnome.org/Projects/GnomeContinuous