Since 1.4.0 rc1 I get "../matplotlib/artist.py:686: UserWarning: Rasterization of 'matplotlib.collections.PolyCollection object at 0x6004a90' will be ignored" when using the rasterized=True parameter on a PolyCollection.

This is due to the fact that PolyCollection doesn't have its own draw method anymore (which in 1.3.1 had the @allow_rasterization decorator) but instead uses the inherited one from _CollectionWithSizes which doesn't have the decorator.