"dm-tool add-nested-seat" doesn't work normally

[Vincent Robin]

Hello,
since I installed Xubuntu 18-04 (on 15 july 2018). The command "dm-tool add-nested-seat" hasn't worked normally. I have a blank screen instead of a login screen. Maybe the problem is due to greeter cause when I set autologin for an user, then everything seems to work normally. The login screen is just skipped.

[Impact]
"dm-tool add-nested-seat" doesn't work (excepted when autologin-user is set).

[Test Case]
1. Log in
2. From a terminal run "dm-tool add-nested-seat"

[Expected result]
A window opens with a login screen

[Observed result]
A window opens with a complete black screen if autologin-user isn't set in /etc/lightdm/lightdm.conf
No error in the terminal.
If autologin is set in /etc/lightdm/lightdm.conf, then it works normally.

[used distribution]
Xubuntu 18-04, up to date.
I didn't have this trouble in may 2018 while I was under Xubuntu 17-10.

[related trouble]
maybe it's related to this bug: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1529454
But I don't exactly have the same trouble. So I thought I should open a new one. Sorry if I was wrong.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.