While looking for a solution for my autoscale issue (see 13/7/2010 16:50) I had a look at the matplotlib (1.0.0) source code and found something strange in axes.py
In the Axes class the method margins()(Line 1651) the doc string says that using margins() with no arguments should return xmargin, ymargin.
If I look at the code for that situation
--- axes.py line (1686-1687)
if not args and not kw:
return self._ymargin, self._ymargin
the ymargin is returned twice.
I suppose that this is a bug and should be
return self._xmargin, self._ymargin