Again, a no brainer:
Glad you found the answer 
See also Fernando's matshow command in CVS. The data scaling with
aspect='preserve' in imshow is currently broken -- the axes
coordinates on the shorter dimension are wrong and because of this
zoom to rect doesn't do what it should. Fernando's command works
around this problem by creating a figure and axes with the proper
aspect ratio . Currently, it only works with arrays, but you could
easily patch it to work with pil images as you did for imshow.
Cheers,
JDH