1st order filter output
Matlab results.

The filters coefficients have a big dynamic variation. So you have those results. For second filter, coefficients b are about zeros.

The first filter

b = [-1.40374673978609e+008 1.40374675978609e+008];
a = [1 1.000000235752411];
freqz(b, a)




The second filter

b = [2.22044577169459e-016 2.22044632680604e-016];
a = [1 -1];
freqz(b, a)