Your application crashed after the resize event. So it never gets repainted and for this you get this behavior (also from your other post).
I do not know exactly why it crashes (i am not this familiar with wxWidgets), but a fix is to remove the inner sizer. I think because the inner sizer has no child it can not calculate the minimal size (or perform any resizing operation) and for this it crashes (some invalid pointer to the non existent child window (only assumption, no knowledge, this is outside from the scope of this forum))...
If you remove the inner sizer all works as expected and you don't get any crash...
The layout of NewFrame:
+ NewFrame
- wxFrame
- wxBoxSizer: BoxSizer1
- wxPanel: Panel1