Wallpaper no longer updates when overwriting wallpaper file?

Issue Description

Until a few months ago, I could change my wallpaper by overwriting the wallpaper file. (I use a wget script that downloads an image from a webserver a few times each hour.) Now, I have to go into Desktop Settings, click away from the current image, and click back on it.

I'm trying to determine whether this is a settings issue on my end, or whether this is an expected behavior change with XFCE (and I should add a "use the new file" line in my script).

This is a headless server over xrdp, single window/monitor; all workspaces affected. I have not had time to hook up I/O to test a local login. I checked with xrdp and they confirmed they did not make any relevant changes.

I believe this happened after a scheduled system update in Arch (I do these manually every week or two), but I did not note when I first noted the change nor what had recently been updated. I have not found any similar issues on the internet, and the issue has not fixed itself after additional updates.

Steps to Reproduce Issue

Locate the current wallpaper file
Copy any other usable background image into the same file
Observe that the wallpaper on the desktop does not change

Expected Behavior

Previously, the wallpaper would change when the file changed.

Additional Information

This is the current behavior: opening Desktop Settings shows a different (new) thumbnail from the (original) wallpaper. The blue highlight confirms that thumbnail is for the file currently set as the wallpaper.

Clicking any other wallpaper image updates the wallpaper as expected.

Environment & Versions

OS distribution and version: Arch
Overall Xfce version: 4.20
xfdesktop version (git hash if not a release): 4.20.1
Windowing system (X11/Wayland): x11
GTK Theme: Adwaita
Icon Theme: elementary
UI Scale Factor: 1.00