I just noticed a small change in behavior with 3d plots. If one creates the plot in the old way (i.e., “ax = Axes3D(fig)”), the plot will start out using the entire figure region as it should. However, once you start to manipulate it (rotate or whatever), the plot loses its horizontal extent (but not vertical extent). The horizontal extent it switches to matches the default extents for regular subplot axes.
I am sure there is partly some sort of issue in mplot3d that is triggering this, but I have to wonder if this would impact anybody else using custom extents for their axes objects.