Created attachment 105798 [details] screenshot of the issue Also on Plasma 5.9. When "Mark applications that play audio" is active, and the taskbar is set to the left or right the application icon is resized outside the bounderies. I can also re-create this with Chromium, Cantata and Telegram.
Created attachment 105799 [details] Plasma theme tasks.svg It could be related to some plasma-themes widgets/tasks.svg file. This one is known to create this behavior
Is this still a problem? I could not reproduce on 5.17 and was changed on 5.18.
Yep, this is definitely fixed now.