Problem with notebook sizing in wx.lib.agw.aui

Hello,

I am using wxpython phoenix 4.0.0b2 with Python 3.6.4 on windows 7
I have added a notebook to an Aui manager application, and it looks fine until I try to resize, bu it will not resize with the other panes.
Not sure what I need to do here.

Code is attached

minimal.py (4 KB)