Why does the FILTFILT documentation not mention the effects of truncation

close all;

[b,a] = butter(5,0.5); 
% a = 1;
delta = [zeros(2,1);1;zeros(100,1)]; % Short Input vector
y_short = filtfilt(b,a,delta);
Y_short = fft(y_short,2048);

delta_long = [zeros(1024,1);1;zeros(1023,1)]; %Long Input vector
y_long = filtfilt(b,a,delta_long);
Y_long = fft(y_long,2048);

figure; impz(b,a,length(delta)); hold on; plot(sqrt(abs(y_short)),'r'); 
figure; impz(b,a,length(delta_long));hold on; plot(sqrt(abs(y_long)),'r');

w = linspace(0,2*pi,length(delta));
wl = linspace(0,2*pi,length(delta_long));
h1 = freqz(b,a,wl);
figure; plot(wl,abs(h1)); hold on; plot(wl,sqrt(abs(Y_short)),'r'); hold off;
h_long = freqz(b,a,wl);
figure; plot(wl,abs(h_long)); hold on; plot(wl,sqrt(abs(Y_long)),'r'); hold off;