AD9833 high freq problem

Hi,

i'm trying to use an ad9833 with MCLK of 16,384Mhz.

Everythings works fine up to 1Mhz but over 1Mhz the output is unregular (sin and tri) and over 2Mhz there is no more a definite sin output

i thought with MCKL 16,348MHz i would be able to have at least 5MHz output.

is it correct?