I think its because wxPopupWindow is
A special kind of top level window used for popup menus, combobox popups and such.

Others think this behaviour is a bug
popupwindow site:wxwidgets.org
[ 1067399 ] wx.TextCtrl on wx.PopupWindow

In reply to Re: TextCtrl and Popupwindow ? by Anonymous Monk
in thread TextCtrl and Popupwindow ? by Anonymous Monk

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