Android :: SensorManager Strange Behaviour Of GetOrientation

I need to retrieve the orientation of my phone. At the moment i wrote this :

CODE:................

This code allows me to get the orientation of the phone if i leave the phone on a flat surface and i rotate it over the surface.

What i did not understand is why if i move the phone upwards the value of this.actual_orientation[0] ,which is the rotation on the zed axis as described [here][1], the value increases although there was no rotation.

Did someone know what happens?

Another strange thing..

I tried my application in the office at work and it had the strange behaviour i described before..
I tried in the same office(same situation) a compass app that i took from the market and it has the same behaviour of mine..when i moved the phone upwards the value changed consistently..
I tried in the same office(same situation) the i-phone compass and it didn't have that strange behaviour!

Then when i arrived at home i tried both, my application and the compass app of my android phone, and they worked!even if i move upwards the phone the value are stable...