erroneous bw bandpass output with constant input

[ChrisHul]

filter_def = create_bw_band_pass_filter( 2, 100, 0.1, 10);

for(uint16_t i = 0; i < 1000; i++) {
output = bw_band_pass( filter_def, 1.0);
}

printf( "output: %f\r\n", output);
//-------------------------------------------------------
yields: "output: 1.00000" expected output: 0.00000 since input remains constant

create_bw_high_pass_filter( 2, 100, 0.1) behaves correctly