Sidechain input changes when I add a new sidechain to a mixer

When I have a Kick on Mixer 1 ; Bass on Mixer 2 and Snare on Mixer 3 and I add a sidechain from the Kick to the Bass mixer. Then I go to settings in Kickstart and add my sidechain input. When I add my second sidechain from my Snare to my Bass mixer the sidechain input on my Kickstart changes from Kick to snare. Why is that and is there a way to fix that. ( This happens with ProQ3 aswell)