[Q] Xiaomi Pistons' volume buttons work as mic button and don't set the volume topic

Hello everybody :)
I bought the Xiaomi Pistons 2 and tried to plug them in my Nexus 7 (2013). They sound good, but the volume buttons don't work as they could. All buttons act like mic button (one tap: play/pause; double tap: skip song). How can I make work them correctly? I'm running CM11 Snapshot 12 and, obviously, the tablet is rooted.