In class Axes (current CVS), there is an instance variable self.legend as well as a method legend(). For some reason, this seems to work most of the time, but I found this problem when I did something like:
ax = subplot(111)
(A "cannot call NoneType"-type error occurs).
Anyhow, changing all occurrences of self.legend to self._legend in Axes.py fixes my problem, but perhaps there are subtleties I'm not aware of? If I don't hear any objections, I'll commit these changes in a day or two.