I have the ST16 controller (ST16 – Yuneec) and the drone is the H520, first model (H520E/520 – Yuneec).
As you can see on the picture, when I move the J2 stick (and only J2), J3 moves also. And when I calibrate sticks, I can't do it for J3, but I can calibrate other sticks.
Hope this will help...