Line spanning visible range with points outside range is missing

[Daniel J Sebald]

I'm running Octave with Gnuplot and find the following:

axis([20 30 0 50]);
plot([1:50],[1:50],'r',[1 50], [25 25], 'g');
figure;
plot([1:50],[1:50],'r',[20 30], [25 25], 'g');

The first plot command does not show the green line, while the second plot 
command does.  Is this proper behavior?  If not, can someone help identify 
quickly if this is an Octave or Gnuplot issue?  Otherwise I'll investigate 
later.

Dan