Hi nureon

!
It's probably because the gesture for switching from volume to pan is a bit close to the one used for muting.
I see two "solutions" for that :
1) Make sure the finger staying on the track you want to mute doesn't move while you are double taping with the other one. That's what triggers the volume -> pan change.
2) If you use quantized mute, you can use the quantized mute shortcut. Simply tap at one end of the track you want to mute, and that will trigger the quantized mute.
Hope this helps

Raphaël