After complex FIR filter, why the spectrum real part and imaginary part is different from original spectrum？

N=18000;

% y0 is a symmetric signal and has N points ;

% FIRfilter is a function by fdatool

% complex bandpass FIR filter--254 orders

Hd=copy(FIRfilter);

Hd.Numerator=Hd.Numerator.*exp(1j*893*2*pi*laser.*(0:254));

% phase delay compensation

m1=zeros(1,127);

% filter apply

y1=filter(Hd,[y0 m1]);

y2=y1(128:18127);

% fftshift

y00=fftshift(y0);

y02=fftshift(y2);

S0_M=abs(fft(y00));

S0_R=real(fft(y00));

S0_I=imag(fft(y00));

S2_M=abs(fft(y02));

S2_R=real(fft(y02));

S2_I=imag(fft(y02));

S0_M==S2_M

But S0_R is different with S2_R，and S0_I is different with S2_I,

How can make the real part and the imaginary part same such as S0_R==S2_R, S0_I==S2_I ?