servo signal issues

I have observed a strange behaviour in the servos output. I'm working with BeagleBone + PXF and I have compiled the current master branch.

The motor suddenly starts to accelerate or decrease the speed. It's possible to fly but the quadricopter is moving in a weird way (changing yaw constantly). It's possible to appreciate this problem just listening the noise of the motor or just simply looking the rotation of the propeller.

In the following graph we can appreciate the correct servos output (this is an old log)
![motor_normal](https://cloud.githubusercontent.com/assets/1933907/4769352/b111d756-5b78-11e4-8301-105344693814.png)

In the following graph I can observe the strange behaviour. It's possible to observe picks. It's producing fast accelerations and decelerations in the motors.
![acelerones_motor](https://cloud.githubusercontent.com/assets/1933907/4769356/c1484bdc-5b78-11e4-9a7e-c2db02833ef1.png)

I also see something strange in the desired roll and desired pitch

![issue_pitch](https://cloud.githubusercontent.com/assets/1933907/4769359/cef50310-5b78-11e4-8efd-8761a7b0acb5.png)
![issue_roll](https://cloud.githubusercontent.com/assets/1933907/4769360/cef80042-5b78-11e4-9286-69f58a2220c1.png)