Bug#1113872: gpsprune: Generic blue application icon in Gnome

[debian]

OK, I found a solution, but I'm not sure whether it's a bit hacky or not.

First, I'll repeat the problem description in case it wasn't clear first 
time:

With a Live USB Trixie session, by default this comes up with Gnome and 
Wayland. If I install GpsPrune (25.2) and choose to run it, then the 
icon _does_ appear properly when I select which application I want to 
start. The desktop file specifies the icon and as you said the icon is 
properly installed in /usr/share/icons, so the "what do you want to 
launch" part is happy to find the icon.

Then I run it, and once it is running, only the generic blue diamond / 
cogs icon is shown. When I switch applications with Alt-Tab, when I 
mouse to the top left to see an overview of what's running, only the 
blue icon is shown and not the Prune icon.

I switch from Wayland to X11, restart GDM, and it has no effect. System 
properties say it's now using X11, env says it's using X11, but the 
behaviour is the same. If it's looking at what's installed, it finds the 
icon, if it's looking at what's currently running then it doesn't - 
maybe it's forgotten how the running application was started?

I then edit the gpsprune.desktop file to include an additional line:

StartupWMClass=tim-prune-GpsPrune

and then restart GpsPrune, and the icon is properly shown everywhere.  I 
have no clue why this line is needed for Trixie's Gnome to find the icon 
when it apparently wasn't necessary for earlier versions.

Hope that helps someone, it seems to be a general problem for many 
applications, many of them java but maybe not all.