AD9172 analog output behaviour

Hi,

I'm configuring AD9172 16bit, 1x interpolation (mode 11).

I observed the following behavior: Sending by JESD all code samples in the interval [0x0000 to 0x7fff]  the waveform is correctly viewed in the oscilloscope.

The same happens if code samples are in the interval [0x8000 to 0xffff]. 

But if the samples are in [0x0000 to 0xffff] crossing the code 0x8000 the output is not correct anymore.  

Is there an explanation?

Thanks