The following code is failing with a segfault on Mac and Linux with backend : Qt4Agg and qt4.backend : PySide.

import matplotlib.pyplot as plt
plt.plot(range(10))

Setting qt4.backend to PyQt4 does not produce a segfault and this code works as expected.
Running %matplotlib in ipython also prevents this segfault.

I have reproduced this on both Enthought and Anaconda releases of matplotib 1.5.0 on Mac (OSX 10.11) and Linux (Ubuntu 14.04).