When I use blueman-applet to connect my external, bluetooth a2p speakers, it's very often that pulseaudio switch to it, so I have sound there, but main channel of kmix is still "built in audio". 

So I have to:

1. rclick on kmix icon, choose "select main channel", 
2. choose BT Logitech (my a2p adapter), click ok, 
3. adjust volume 

When BT mixer is muted, then it's less annoying. But sometimes, BT mixer is NOT muted, and music I put there is very loud, and there is night and before I mute/lower volume it using 1-3 procedure described above, everyone is on their feets shouting "what are you doing man!". Not funny. 

Reproducible: Always

Steps to Reproduce:
1. rclick on blueman manager on a2p device, choose "connect with mixer audio". 
2. try to change volume using kmix
Actual Results:  
Nothing. Kmix changes volume of previously used mixer. 

Expected Results:  
Kmix should change volume of right-connected a2p device.