Bug#785318: gdm3: Cancel button does nothing when prompted to type an unlisted username

[George Bateman]

Package: gdm3
Version: 3.14.1-7
Severity: normal

Dear Maintainer,

I started my computer and was presented with the GDM login screen. I 
clicked "Not listed?" and was prompted for a username. I then clicked 
"Cancel" but I was not returned to the main menu; nothing visible happened
at all.  I therefore typed my username into the box and clicked Next. I was
prompted for my password, and the "Cancel" button on that page worked,
and returned me to the main menu.

The bug can also be produced if Gnome is locked from the power menu and
you try to log in as a different user. 

Thank you for an otherwise nice piece of software!

George Bateman.

-- System Information:
Debian Release: stretch/sid
  APT prefers testing-proposed-updates
  APT policy: (500, 'testing-proposed-updates'), (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.16.0-4-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.utf8, LC_CTYPE=en_GB.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gdm3 depends on:
ii  accountsservice                       0.6.37-3+b1
ii  adduser                               3.113+nmu3
ii  dconf-cli                             0.22.0-1
ii  dconf-gsettings-backend               0.22.0-1
ii  debconf [debconf-2.0]                 1.5.56
ii  gir1.2-gdm3                           3.14.1-7
ii  gnome-session [x-session-manager]     3.14.0-3
ii  gnome-session-bin                     3.14.0-3
ii  gnome-settings-daemon                 3.14.2-3
ii  gnome-shell                           3.14.4-1
ii  gnome-terminal [x-terminal-emulator]  3.14.1-1
ii  gsettings-desktop-schemas             3.14.1-1
ii  libaccountsservice0                   0.6.37-3+b1
ii  libaudit1                             1:2.4-1+b1
ii  libc6                                 2.19-18
ii  libcanberra-gtk3-0                    0.30-2.1
ii  libcanberra0                          0.30-2.1
ii  libgdk-pixbuf2.0-0                    2.31.1-2+b1
ii  libgdm1                               3.14.1-7
ii  libglib2.0-0                          2.44.0-2
ii  libglib2.0-bin                        2.44.0-2
ii  libgtk-3-0                            3.14.5-1
ii  libpam-modules                        1.1.8-3.1
ii  libpam-runtime                        1.1.8-3.1
ii  libpam-systemd                        215-17
ii  libpam0g                              1.1.8-3.1
ii  librsvg2-common                       2.40.5-1
ii  libselinux1                           2.3-2
ii  libsystemd0                           215-17
ii  libwrap0                              7.6.q-25
ii  libx11-6                              2:1.6.3-1
ii  libxau6                               1:1.0.8-1
ii  libxdmcp6                             1:1.1.2-1
ii  libxrandr2                            2:1.4.2-1+b1
ii  lsb-base                              4.1+Debian13+nmu1
ii  metacity [x-window-manager]           1:3.14.3-1
ii  mutter [x-window-manager]             3.14.4-2
ii  openbox [x-window-manager]            3.5.2-8
ii  policykit-1                           0.105-8
ii  ucf                                   3.0030
ii  x11-common                            1:7.7+8
ii  x11-xserver-utils                     7.7+4
ii  xterm [x-terminal-emulator]           318-2

Versions of packages gdm3 recommends:
ii  at-spi2-core               2.14.0-1
pn  desktop-base               <none>
ii  gnome-icon-theme           3.12.0-1
ii  gnome-icon-theme-symbolic  3.12.0-1
ii  x11-xkb-utils              7.7+2
pn  xserver-xephyr             <none>
ii  xserver-xorg               1:7.7+8
ii  zenity                     3.14.0-1

Versions of packages gdm3 suggests:
pn  gnome-orca            <none>
ii  libpam-gnome-keyring  3.16.0-2

-- debconf information:
* shared/default-x-display-manager: gdm3
  gdm3/daemon_name: /usr/sbin/gdm3