This bug was fixed in the package gdm3 - 3.28.2-2ubuntu1

---------------
gdm3 (3.28.2-2ubuntu1) cosmic; urgency=medium

  [ Iain Lane ]
  * Merge with Debian. Remaining changes:
    + README.Debian: update for correct paths in Ubuntu
    + control.in:
      - Don't recommend desktop-base
      - Depend on bash for ubuntu_config_error_dialog.patch
      - Update Vcs field
    + rules:
      - Don't override default user/group
      - --enable-gdm-xsession to install upstream Xsession script
      - override dh_installinit with --no-start to avoid session being killed
    + rules, README.Debian, gdm3.8.pod:
      Use upstream custom.conf instead of daemon.conf
    + gdm3.{postinst,postrm}: rename user and group back to gdm
    + gdm3.postinst: don't kill gdm on upgrade
    + gdm3.*.pam: Make pam_env read ~/.pam_environment
    + gdm3.install:
      - Stop installing default.desktop. It adds unnecessary clutter
        ("System Default") to the session chooser.
      - Don't install debian/Xsession
    + Add ubuntu_run_xsession.d.patch
    + Add ubuntu_xresources_is_a_dir.patch
      - Fix loading from /etc/X11/Xresources/*
    + Add ubuntu_nvidia_prime.patch:
      - Add hook to run prime-offload (as root) and prime-switch if
        nvidia-prime is installed
    + Add revert_override_LANG_with_accountservices.patch:
      - On Ubuntu accountservices only stores the language and not the
        full locale as needed by LANG.
    + Add ubuntu_dont_set_language_env.patch:
      - Don't run the set_up_session_language() function, since it
        overrides variable values set by ~/.pam_environment
    + Add ubuntu_config_error_dialog.patch:
      - Show warning dialog in case of error in ~/.profile etc. and
        don't let a syntax error make the login fail
    + Add debian/default.pa
      - Disable Bluetooth audio devices in PulseAudio from gdm3.
    + debian/gdm3.install
      - Added details of the default.pa file
    + debian/gdm3.postinst
      - Added installation of default.pa and creation of dir if it doesn't
        exist.

  [ Marco Trevisan (Treviño) ]
  * debian/patches/ubuntu_nvidia_prime.patch:
    - Fix install file paths

gdm3 (3.28.2-2) unstable; urgency=medium

  * debian/patches/libgdm-drop-support-for-serializing-multiple-opens.patch,
    debian/patches/libgdm-fix-pointer-boolean-task-confusion.patch,
    debian/patches/libgdm-don-t-keep-manager-proxy-around-longer-than-we-nee.patch,
    debian/patches/libgdm-use-g_object_unref-instead-of-g_clear_object-for-w.patch,
    debian/patches/libgdm-get-connection-explicitly.patch,
    debian/patches/libgdm-Drop-weak-refs-on-the-GDBusConnection.patch,
    debian/patches/libgdm-Unref-the-manager-propagated-from-task.patch,
    debian/patches/libgdm-Don-t-double-ref-the-connection-got-from-task.patch,
    debian/patches/libgdm-Don-t-leak-connection-on-sync-re-authentication.patch,
    debian/patches/libgdm-Use-auto-pointers-and-cleanup-code.patch,
    debian/patches/libgdb-Try-to-reuse-connections-from-the-available-proxie.patch,
    debian/patches/libgdm-Don-t-save-manager-address.patch,
    debian/patches/libgdm-Return-NULL-on-invalid-client-instances.patch:
    - Cherry picks commits from upstream 3.28 branch to propely fix ref-counting
      issues on GdmClient (LP: #1766137)

 -- Iain Lane <email address hidden>  Tue, 05 Jun 2018 10:11:10 +0100