Spanning Screens desktop backgrounds issue when resuming from DPMS sleep state.

Issue Description

On a two monitor setup with the second monitor on the left of the main both the screens desktop images are blank after resuming from sleep when a single background image is selected and it's style is set to "spanning screens"

Steps to Reproduce Issue

  1. Set up two monitors, the second monitor to the left of the main.
  2. Using the Desktop app select a background on the main monitor and set its style to "Spanning Screens"
  3. Move the Desktop app to the left screen and select the style "None"
  4. The chosen background should now be spanning both screens.
  5. Using the Power Manager select a suitably low time of 1 minute for the screens to sleep.
  6. Wait for the screens to sleep and go black. Continue to wait unit monitors popup a signal message warning about losing connection.
  7. Wake the system with the mouse or keyboard.
  8. Notice both screens are now black.
  9. To recover the background images repeat steps 2 and 3. You may have to cycle "Apply to all workspaces" check box on each monitor to recover the images.

Expected Behavior

It should be expected the chosen desktop background image remains after waking from sleep.

Additional Information

Screen saver disabled. So not a factor.

If the screens are woken before the monitors signal message warning the desktop images may be preserved.

If the monitors are set to the same background but without spanning the issue does not manifest.

Environment & Versions

  • OS distribution and version: Arch Linux x86_64
  • Overall Xfce version: Xfce4 4.20
  • xfdesktop version (git hash if not a release): 4.20.1
  • thunar version (if issue related to file/launcher icons): n/a
  • Windowing system (X11/Wayland): X11
  • Compositor and version (if Wayland): n/a
  • GTK Theme: Adwaita-dark
  • Icon Theme: Elementary
  • UI Scale Factor: No Scaling