Why are the results (A0, B0, C0 and D0) of the following code different for Matlab R2011b (32 bit) and Matlab R2015a (32 bit)? amx661.mat is attached.

clc;
clear all;
close all;

%ARMAX MODEL PARAMETERS
load amx6661; %loading the identified model
amx_model=amx6661;
Ts=0.75;

%CREATION OF REFERENCE TO BE TRACKED AND NOISE
Ns=2000; %number of simulation points
e=0.00001*ones(Ns,1); %creating noise
r=1*ones(Ns,1); %set point to track

%converting armax model to state-space model of the form:
%x(k)=A0x(k-1)+B0u(k-1)+G0e(k-1)
%y(k)=C0x(k)+D0u(k)+e(k)

G_id=idss(amx_model);
A0=G_id.A;
B0=G_id.B;
G0=G_id.K;
C0=G_id.C;
D0=G_id.D;