touchscreen problem introduced on upgrade of xorg-server and xorg-server-common from 1.20.x to 21.1.x

Until recently, when using my touchscreen laptop with arch/xfce4, touching xfce4-panel plugins would cause the menus to open, and then I could choose items from the menu. For example activating a VPN network, or changing wifi connection.

After upgrading these packages, this behavior stopped working with several of the plugins.

xorg-server (1.20.13-3 upgraded to 21.1.1-3)
xorg-server-common 1.20.13-3 upgraded to 21.1.1-3)

I've observed the problem with: pulseaudio, power manager, notifications, and anything in the status tray, most notably wifi and bluetooth. (Some other plugins, such as the clock, still work correctly.)

Now when I touch one of these plugins, the menu will open while my finger is touching the screen. But as soon as I remove my finger from the screen, the menu immediately closes. I can see the contents of the menu, but can't interact with them. Even if I try sliding my finger along the menu, while the menu stays open I'm unable to select anything, and as soon as I lift my finger from the screen the menu immediately closes.

Reverting these packages fixes the problem (the menus stay open on touch).

Here's a screen shot of one of the plugins/menus affected, for reference. After the upgrade, this power manager plugin will only stay open as long as the finger is actually touching the screen, and immediately closes when the finger is removed. Before package upgrade, touching the power icon caused the menu to toggle open (and stay open). A second touch would toggle the menu closed, or you could touch to change brightness or presentation mode, etc.

I'm not sure if this would be a bug that has been introduced, or if it's caused by an API change that hasn't been implemented in the xfce4-panel project. Thanks in advance for any help!