Why does the cascade of a lowpass and a highpass Butterworth filter not produce the same

Why does the cascade of a lowpass and a highpass Butterworth filter not produce the same results as a bandpass Butterworth filter in Signal Processing Toolbox 6.10 (R2008b) ? I created a cascade of lowpass and highpass Butterworth filters and compared the result to a bandpass Butterworth filter - all created using either the Signal Processing Toolbox or the Filter Design Toolbox.   The following is an example of this process: %%8th order bandpass filter [b,a]=butter(4,[0.4 0.6],'bandpass'); Hbp=dfilt.df1(b,a); %%Cascade of 4th order lowpass and highass filters [b1,a1]=butter(4,0.6); % Lowpass [b2,a2]=butter(4,0.4,'high'); % Highpass H1=dfilt.df1(b1,a1); H2=dfilt.df1(b2,a2); Hcas=dfilt.cascade(H1,H2); I expected "Hcas" and "Hbp" to be equivalent filters. However, executing the following command shows that this is not true:     fvtool(Hbp,Hcas)