tutorial1.py (saving plot to png) does not work (Ubuntu 16.04, Chaco 4.6.0dev181)

The first execution of

https://github.com/enthought/chaco/blob/master/examples/tutorials/tutorial1.py

results in a segmentation fault:

``` python
/usr/lib/python2.7/dist-packages/chaco/array_data_source.py:123: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._data = newdata
/usr/lib/python2.7/dist-packages/chaco/axis.py:498: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
for tickpos in mapped_tick_positions]))
/usr/lib/python2.7/dist-packages/chaco/axis.py:499: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._tick_label_list = tick_list
/usr/lib/python2.7/dist-packages/chaco/axis.py:500: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._tick_label_positions = self._tick_positions
Please enter a path in which to place generated plots.
Press to generate in the current directory.
Path:
Creating image: /home/paul/repos/chaco/examples/tutorials/tutorial1.png
Segmentation fault (core dumped)
```

The second execution (when tutorial1.pyc exists) does not segfault, but produces an empty (white) image (tutorial.png, 501x501px).

Exporting to PDF files works with my current setup.