Thank you guys!
After testing in the field the "rudder effect" of the differential spoilers is not working as expected (it causes the plane to dive violently to the desired side). I asume that this is why people says that differential spoilers are not working.
Differential spoilers at this moment only aplies mixing for 2 surfaces (if you yaw left, only left elevon and left "flap" are affected) and I suspect that only drag effects are programmed, not any "elevation compensation" is included, and definitely the stabilisation of the board cannot handle the results.
Also I couldn't find any parameter to calibrate the differential spoiler mixing (other than the mixing itself), so I couldn't play too much testing.