Polarisation and k vector are not vertical to each other

Hi

I try to simulate a waveguide and I see that the polarisation vector and the k vector are not orthogonal.

I did it by the attachment mph file and taking the data into a MATLAB script to take a dot product between the vectors to check if they are perpendicular.

what I have found is that these vectors are not orthogonal excluding in the plane z=0 but in every other place it isn't. which is not expected according to theory.

Is anyone encountered in such similar case?

thanks in advance