zero values of accel X and Y with DMP

Hello,
I‘m working with the MPU6000 with a PIC MCU over SPI interface. I want to use the DMP to generate and read the quaternions. So I implemented embedded_motiondriver_5.1 to my environment. When I don’t turn on the DMP, I’m able to read the raw data on every interrupt of the MPU.

But if the DMP is enabled the datavalues of accel X and accel Y of dmp_read_fifo(...) value is always zero. The accel Z and all gyro values are okey. The quaternions are completly out of range, but I think the reason for that are the zero values in accel X and Y.

How is that possible? Thanks for help.