What were you trying to do that didn't work?

Customer has configured XDMCP on a remote server which they intend to use with RealVNC Viewr or TigerVNC Viewer. However, the GDM login screen only displays one(first) user account when connected through XDMCP. For logging into other user accounts, customer is having to user the "Not listed?" option. 

This is happening  even when other user accounts have already logged in to the machine to be populated on the GDM login screen.

Tried using the dconf setting below - But it did not make any difference.

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[org/gnome/login-screen]

disable-user-list=false

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How reproducible:

Always with XDMCP sessions in customers environment.

Steps to reproduce

1. Configure XDMCP on the machine.
2. Connect to the machine using a suitable VNC client viewer
3. Check if more than one account is listed on the GDM login screen.
4. If no, then try logging into another account other than the one displayed on the screen using "Not listed?" option.
5. Logout of the session.
6. Start another XDMCP session. Only the first user account is visible and the other user account we logged into in the above scenario doesn't show up in the gdm login screen list.

Expected results

Customer has two questions -

1) Is this the intended behaviour of XDMCP and if so, can they have the documentation.

or

2) If this is a bug, will this be fixed?

Actual results

Only one use account is persistently being shown on the GDM login screen when connected through XDMCP session.