Widget does not automatically re-render when calling load() after initializing with None

[sc1f]

Bug Report

Steps to Reproduce:

1. Create a PerspectiveWidget, passing in None as the first parameter
2. Rendering the widget.
3. Call load() on the widget with a dataset.

Expected Result:

Widget should automatically re-render with the new dataset visible.

Actual Result:

Widget does not re-render, but it displays properly after manually rendering.