Please note that a static box should not be used as the parent for the controls it contains, instead they should be siblings of each other. Although using a static box as a parent might work in some versions of wxWidgets, it results in a crash under, for example, wxGTK.
Also, please note that because of this, the order in which you create new controls is important. Create your wxStaticBox control before any siblings that are to appear inside the wxStaticBox in order to preserve the correct Z-Order of controls.