The EditorManager's wxNotebook is for the editor--I don't think its related to the problem.
Manager holds a wxSplitPanel (a C::B class) which holds a wxSplitterWindow.
EditorManager and ProjectManager both call the global Manager for the wxSplitPanel which in turn provides the wxSplitterWindow. Each adds their own wxTreeCtrl to the wxSplitterWindow.
I think the problem is specifically with the ProjectManager's wxTreeCtrl, but I am confused as to why? They approach content differently--adding items, building, rebuilding, ext.--but they are similar.