How does axes property DataAspectRatio affect properties Position/TightInset

The documentation for getframe, explains how to calculate a margin so that captured image data includes the title, axis labels, and tick labels. The stated example works fine. However, if I set the axes DataAspectRatio property, this approach does not work anymore. For the specific example from the documentation,

plot(rand(5))
xlabel('x values')
title('Plot of Random Data')

set(gca, 'DataAspectRatio', [1 1 1]); % Added line

drawnow
ax = gca;
ax.Units = 'pixels';
pos = ax.Position;
ti = ax.TightInset;

rect = [-ti(1), -ti(2), pos(3)+ti(1)+ti(3), pos(4)+ti(2)+ti(4)];
F = getframe(ax,rect);

figure
imshow(F.cdata)

I get the following error:

Error using getframe (line 122)
The specified rectangle is not fully contained within the figure. MATLAB no longer supports this capability.

So the questions are:

1. Why doesn't this approach work when DataAspectRatio is set?
2. How can I calculate the margin that includes title, axis and tick labels, when DataAspectRatio is set?