some questions about pll ADF4252BCP.

the vco out frequency is 320~380MHz ,step frquency 1.25KHz.the reference oscillator is 10MHz,R=5,so the PFD =2MHz,all the frequency can lock well ,but when the pll is locking,there is a 344MHz frequency out,the power is -90dbm.when i change the register N,the 334MHz not change ,when i power down the vco,the 334MHz still stands here. my reference oscillator is sine wave ,no harmonics.when i change the PFD=5MHz,the frequency changes.I want to know whether the ADF4252
will oscillator in such frequecy range .how to avoid it?
thanks!

nobody knows?