The sis_filtercascade_15242.xml stationxml file is an example of a filter cascade from SIS where the symmetry of the FIR filter was wrong, generating a response that is not correct. Note the large ripple in the passband. Choosing a channel from IRIS hopefully shows other more correct responses. You may also paste a URL to a stationxml, IRIS stationxml-resp from the NRL, or SIS extended stationxml file into the box to plot it.