LTC5594 I/Q channel DC offset changes with gain/power


I'm using LTC5594 evaluation board and I noticed that once I adjust I/Q channel DC offset to minimise a DC component, the DC component starts to increase  if I change the gain of the LTC5594 or if I change input RF power into the LTC5594. I also measured the common mode voltage at the I/Q port and it changes if the gain of the LTC55594 changes. 

Is this behaviour normal?

Thank you,