AD9957 Output

Hi, I am using the AD9957. I use the Blackfin mode QDUC. On the Q-channel I send 0x8000 and on the I-channel 0x0000. There is no output signal. But if I swap the data to I-channel 0x8000 and Q-channel 0x000 there is carrier visible? This is wierd. Can somebody please help. The CCI filter did not overflow (pin 20).