MLCC Measurement

I am conducting a measurement on the high frequency response of MLCC.
The measurement is done in a self-designed test fixture and using TRL method for fixture calibration. However , i think the result has something wrong. the measured S(1,1) is not equal to S(2,2) while S(1,2) and S(2,1) is exactly the same. Does anyone know what happen on it?

the .S2P of a 4.7pF capacitor is attached