working with AD-FMCOMMS1 at low sampling rate

Hi

I'm using AD-FMCOMMS1 on ML605 (Microblaze) with reference design no-OS (edk 14.4).

When I set the DAC sampling rate to 122.88MHz and higher there is no problem with it. However, if I lower the DAC sampling rate to 92.16MSPS or 61.44 MSPS (and using DDS to make a tone) it seems that it cause a problem. I can see on the spectrum analyzer that the real sampling rate is 1/4 of what I set (note: REG 0x4058 in DAC PCORE (CLK_RATIO) is 4. Could it be related?)

what cause this? Can it be cured?

Bests,

FArid