I don't understand, what KDE does with my sound settings. I have only one sound card on the mainboard and one monitor. This should be a very common setup. But I have two panel symbols. See the screenshots. I removed my complete KDE user configuration. But the situation did not change. Reproducible: Always Expected Results: One symbol.
Created attachment 96793 [details] mixer panel 1
Created attachment 96794 [details] mixer panel 2
After some updates I am still having these two symbols. Now I have platform 4.14.26 and kmix 4.6.
I am closing this bug. Perhaps it is not fixed. But I cannot reproduce it any more.