Bug 449224

SUMMARY
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Please move this to the correct category if this is wrong :-)

STEPS TO REPRODUCE
1. Create a scalable svg or bitmap and place it in /usr/local/share/icons/hicolor/{scalable, 32x32, etc}
2. Launch a program with a .desktop file specifying the name of that icon
3. The icon is shown in the task manager widget correctly, but not in the actual window decoration

OBSERVED RESULT
It's sort of a "blank file" or "not found" icon instead of the actual app icon.

EXPECTED RESULT
The actual app icon.

SOFTWARE/OS VERSIONS
Windows: N/A
macOS: N/A
Linux/KDE Plasma: Fedora Linux 35
(available in About System)
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
I found this while trying to fix PolyMC's icon bugginess while running it Wayland native, and surprised to find this bug! Now, moving the icon file and installing it in /usr is fine, but it's even weirder that the task manager is able to pick it up correctly and not the window decoration (which means the problem isnt the app itself).