Affect of accel can't be eliminated in 6-axis data fusion

Hello,

I configured the MotionApp 2.0 for 6-axis data fusion in order to measure the inclination angle on x axis using MPU-6000, and I can get all the data such as Euler angles and gravity. But I find that the affect of acceleration is not completely eliminated. The value of quaternion changes when I add an acceleration. This variation of value depends on the magnitude of acceleration added. My question is:
Can't we completely eliminate this affect of acceleration or we can just reduce it?

Besides, the rotation perpendicular to the horizontal plane of MPU module can also affect the inclination angle. When I return the MPU module for the yaw rotation, the gravity(inv_get_gravity) on x axis firstly changes to another value and then come back gradually to the original one. Can anyone also explain me this? Thanks in advance.

Yijun