mpu9150 Quaternion Reading drifting

Hi,

I have two sets of devices:
(1) mpu9150 + arduino
the arduino firmware code is downloaded from here https://github.com/sparkfun/MPU-9150_Breakout/tree/master/firmware/MPU6050.
(2) mpu9150 + micaz
micaz firmware is developed under tinyos and we followed the arduino code procedure.

Both devices will transmit quaternion values from mpu9150 to a computer, where we run Teapot application to show device movement.

The problem we have: for micaz set, sometimes motion drifting is noticed. Somehow for arduino set, we didn't see any drifting occur.

Anyone has any comments?