FXList, FXTreeList and getCursorItem

Hi,

I have an application using Fox 1.6 that I build on Windows and Linux, 
and some Linux users have reported that context menus on TreeList items 
no longer work. I cannot reproduce this on Windows, and not on my Ubuntu 
machine, but it happens on a Debian bullseye installation. What's 
happening is this:

I handle the SEL_RIGHTBUTTONRELEASE message and create a FXMenuPane for 
the popup based on the value of getCursorItem, but on this machine, that 
always seems to return null. As a fallback, I can call 
getItemAt(event->click_x, event->click_y) and that also returns the item 
I'm looking for, but

a) this feels like it shouldn't be necessary, and
b) how is it only broken on this one distro?

A similar thing happens in another part of the application with an 
FXList, for which getCursorItem consistently returns -1.

Interestingly, if I run the program so that it sends the display to 
another X server, then getCursorItem works, so could it be a bug in 
xserver-xorg? The one in bullseye is significantly older than the one in 
jammy.

Enno.