Comment 16 for bug 1405349

This is not actually caused by LightDM - when you make the guest session active (via logind) it doesn't appear to detect this and turn the screen on.

To reproduce:
1. Login with your account normally.
2. Switch to guest session from the panel menu "Switch Account... -> Guest Session"
3. Switch back to your user account.
4. Find the guest session ID by running loginctl, i.e.
$ loginctl
   SESSION UID USER SEAT
        c4 1000 bob seat0
        c1 135 guest-4aZrXA seat0
5. Switch to the guest session, i.e.
$ loginctl activate c1

Observed result:
The screen is black until the mouse moves

Expected result:
The desktop is shown immediately