Sorry for the delay, I´ve been off-line these days.
About the sensor mode, I´m using mode 3. I´ve tried all of them and this one seems to be the best one.
The issue is a little bit weird. It´s like the sensor values were mixing slowly. After some minutes if I move the head to one size, the mouse draw a circle. Seems like Google Cardboard is correcting the angles using the accelerometer too.
BTW, if the last version of the server (1.9.1d) the Pitch cannot be inverted.