Magnetometer not working properly on N8 running Belle

I made Qt application which collects data from sensors (accelerometer, magnetometer, proximity, compass, GPS...). I have used application on N8 and it works perfectly on Anna devices. However, there seems to be problem with Belle. It works fine at start (from 5 to 60 minutes) but in some point magnetometers and compass seem to freeze, and I do not get updates to their values. This problem seems to be related with Belle because it works fine on Anna and I've tested the application with two different N8 phones running Belle.

Update: Build using Qt 4.7.4 for Anna and Qt 4.7.4 for Belle, neither works

Update 2: Magnetometer seems to freeze faster under battery save mode