How do I get wlr/taskbar to use icons from windows?

[MrDOS]

wlr/taskbar reuses the same icon for all Wine application windows. The top window here is Mikrotik WinBox, and the bottom is winecfg:

My window manager (labwc) picks up on the windows' icons and uses them correctly in window decoration and the task switcher, but for some reason, wlr/taskbar uses the WinBox icon for every Wine application.

I'm using Waybar v0.14.0-3 as packaged in Arch.

WinBox wasn't installed from a package; it just lives in my ~/.local/bin. I launch it by way of a desktop entry in ~/.local/share/applications/winbox64.desktop:

[Desktop Entry]
Name=MikroTik WinBox
Exec=/home/mrd/.local/bin/winbox64.exe
Icon=winbox64
Terminal=false
Type=Application

The Arch wine package includes suitable binfmt configuration for Windows executables, so the /proc/n/cmdline is just /home/mrd/.local/bin/winbox64.exe.

I don't have a desktop entry for winecfg, so it was launched directly from the command line. Its /proc/n/cmdline is C:\windows\system32\winecfg.exe.

However, both the WinBox and winecfg processes have their /proc/n/exe pointing at /usr/lib/wine/x86_64-unix/wine-preloader.

I wonder if perhaps Waybar tries to be a bit clever, and looks up the icon for each taskbar item from a desktop entry that it thinks corresponds to the window's executable, rather than just using the window's icon directly. After all, the icon referred to by the desktop entry will probably be available in a range of sizes. Is that what's happening here? If so, is there any way to disable this behaviour, preferably for a specific executable?