Bug#925910: mate-desktop: 'Dead zone' on large screen with multi-screen display

[Jasper Taylor <jasper@simulistics.com>]

Package: mate-desktop
Version: 1.20.4-2
Severity: important
Tags: upstream

Dear Maintainer,
Expected behaviour:

To be able to place a window anywhere on either screen

Actual behaviour:

Trying to drag a window to the centre of the larger screen reveals that there
is a 'no-go area' and if you drag right across it, the window snaps to the
other side when exiting this area.

Steps to reproduce the behaviour:

  * Connect two screens to your PC, one wider (in pixels) than the other.
  * Open mate-display-properties. Set the narrower screen as primary, and
position it above or below the wider screen, so the centres of the two screens
are vertically aligned.
  * Apply and click to keep the new arrangement.
  * Now drag the mate-display-properties window (or any small window) across
the larger screen. It cannot be placed in the centre but will snap from one
side to the other.
  * If the left or right sides of the two screens are vertically aligned, the
problem does not occur.

I thought this might be a LightDM problem but it does not occur in Cinnamon or
Xfce desktop so I figure it must be mate-desktop.

Also reported as https://github.com/mate-desktop/mate-desktop/issues/359



-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-2-amd64 (SMP w/4 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages mate-desktop depends on:
ii  hicolor-icon-theme        0.17-2
ii  libatk1.0-0               2.30.0-2
ii  libc6                     2.28-8
ii  libcairo-gobject2         1.16.0-4
ii  libcairo2                 1.16.0-4
ii  libgdk-pixbuf2.0-0        2.38.1+dfsg-1
ii  libglib2.0-0              2.58.3-1
ii  libgtk-3-0                3.24.5-1
ii  libmate-desktop-2-17      1.20.4-2
ii  libpango-1.0-0            1.42.4-6
ii  libpangocairo-1.0-0       1.42.4-6
ii  libstartup-notification0  0.12-6
ii  libxrandr2                2:1.5.1-1
ii  mate-desktop-common       1.20.4-2

Versions of packages mate-desktop recommends:
ii  mate-user-guide  1.20.2-1

Versions of packages mate-desktop suggests:
ii  mate-desktop-environment  1.20.0+5

-- no debconf information