loop stereo can not be disabled

I have loaded the loop stereo in slot "X". When I disable slot X, after 1/2 second, I can hear that the loop is active again, although the status is "off".
Is this a known bug, or may I be doing something wrong?
I have connected the Kemper send with the input of my SY-300 guitar synthesizer, and the main output of the SY-300 goes into the alternative input and the return input of the Kemper. It's pretty easy to tell when the signal of the SY-300 is on...

What is the aux volume? Or where can I turn it down?

I found this in the manual:
Both the RETURN and the ALTERNATIVE IN can also be used as auxiliary inputs. You could, for instance, use this feature to mix in music from your mp3 player and play along. You will find the corresponding mix controls in the Output/Master Section.
But I don't see any mix controls on the Output Volume page that refer to aux volume.

Ooops. Ok, I see it now...
Turning down the aux in did solve the problem.

IMO the aux in volume should be automatically set to zero when the loop stereo is inserted in a slot. I cannot imagine a scenario where I still want to hear the effects loop when the slot where it is inserted is disabled.