plasma-pa causes an empty space to be created in the systray next to the applet. Disabling plasma-pa makes it disappear, but a non-functional plasma-pa icon remains. Reenabling it makes the working icon reappear, but a non-functional icon remains next to it. Reproducible: Always
Created attachment 94089 [details] After startup
Created attachment 94090 [details] after disabling plasma-pa. The volume icon doesn't do anything
Created attachment 94091 [details] after reenabling plasma-pa. Note that kmix is not running in any case, so it's not the cause of the extra icon.
I have the same issue, this seem to be happening randomly.
*** This bug has been marked as a duplicate of bug 347554 ***