This looks tangentially related to a problem I've just noticed - in axes.py, the pie graph code doesn't assign the label strings it was given to the 'pie segment' Wedge patches it generates.
With the change shown below, it does:
for frac, label, expl in zip(x,labels, explode):
w = Wedge((x,y), radius, 360.*theta1, 360.*theta2,
I noticed this problem while trying to generate a legend, same as Emmanuel - could the scatter plot code have a similar problem? Or am I looking at something completely different?
(Incidentally, I've noticed that the shadow patches generated by the pie code are also included in the legend - this doesn't look like the right behaviour, but I'm still very new to matplotlib, so I'm not sure.)
(The code above is from the python2.3-matplotlib v0.86.2-4 debian package.)