Bug 418742

SUMMARY

I have icons-only task manager setup and the restore Plasma session activated.
As effect, several (four in this case) Dolphin instances are restored at startup.

OBSERVED RESULT

I have started two VLC instances and a Firefox instance.

Firefox has no mute button on its icon.

The multiple instances are collapse in one icon on the icons-only task manager bar.

Dolphin icon has a mute button.
VLC icon has a mute button.

The bug consists in the fact that the mute button of Dolphin icon has effect over the first opened instance of VLC and that only.
The mute button on the VLC icon seems to affect nothing (I don't have an instance of some application to be muted by it, apparently).
Closing the second VLC instance removed the mute button from the Dolphin group icon.

Also, its unclear which instance the mute button should operate on which instance, as there are many, but seems to work on one only.
It's unclear if it is icons-only task manager related too.

STEPS TO REPRODUCE

Not sure of the sequence to open the instance of what application to get to the problem yet.

EXPECTED RESULT

The mute button should be assigned to a specific instance of an application or group of some kind and manage the application whose the icon belongs to.

SOFTWARE/OS VERSIONS

Operating System: Gentoo Linux 
KDE Plasma Version: 5.18.1
KDE Frameworks Version: 5.67.0
Qt Version: 5.14.1
Kernel Version: 5.4.0-sabayon
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7 CPU 920 @ 2.67GHz
Memory: 23,5 GiB of RAM

ADDITIONAL INFORMATION