in v1.4.2 the line
_affine = transforms.Affine2D
is removed but immediately used in collections.py, around line 1480.

    if self._units == 'xy':
        m = ax.transData.get_affine().get_matrix().copy()
        m[:2, 2:] = 0
        self.set_transform(_affine(m))

This gives a name error when trying to show the figure inline in ipython notebook, and siliently fails (dumps nothing) for Figure objects. -- if a collection is added to the axes.