Icon weirdness with grouped window list applets

I’ve tried (2) different grouped window list applets - the default one and CobiWindowList - and both suffer the same glitch. This seems to be specific to web apps (so far tested with Brave). Whenever I open my first web app, the icon is displayed properly. However, every single one after that always uses the first icon.

Has anyone else seen this?

EDIT: just tried (2) others, both exhibit the same behavior. Guess I’ll post a bug report with Cinnamon.