MuseScore Icon behaves weird in Alt+Tab on Linux

Hello, I am using the latest version of MuseScore on Arch Linux. I have downloaded MuseScore from the official repositories with pacman.
MuseScore is working properly so far, except one thing that drives me nuts: The icon for the Alt Tab menu is a bit weird...

As you can see in the screenshot, the icon in Alt Tab is not only very low resolution, it also is not even round as it is supposed to be. On the left side of the screenshot you can see a desktop link to MuseScore which has the proper icon. In the file explorer you can also see that there is the proper mscore.svg icon in the location of my icon theme (the .svg is a round musescore icon).
However still the Alt Tab icon is different from the others. But i want it too be high resolution and round. What do I have to do for this?
I literally ran a "find" command through my entire drive which found all mscore/musescore.svg/.png's, but the only icon that isn't round is one that is used somewhere in the manual, but doesn't look quite like the Alt Tab one. So why does the Alt Tab entry use such a weird icon, and where the hell does it get the file from?

Edit: I am using the latest KDE as desktop environment, if it matters...
But for me it looks like a problem in MuseScore itself here, because no other application behaves like this

Edit2: Hell, I even followed the "open" syscalls via strace, but I didn't find any square musescore icon that it opens. It seems to me, that this icon is somehow hardcoded into the application... I would really appreciate an answer to this topic. :)