With current development tip, matplotlib hangs with an error

 matplotlib-2.0.0+3906.ga95a2789e-py3.5-linux-x86_64.egg/matplotlib/transforms.py:655: RuntimeWarning: invalid value encountered in less
((self.min < vertices) & (vertices < self.max)).all(axis=1).sum())

After this, the plots remain on screen (I'm using spyder as a development front end), but the buttons on the plots are inaccessible and it is impossible to save the graphs.

The code used to work with 1.5.3 and also used to work with head of devel branch until a few days ago.