(inkscape:599): Gtk-WARNING **: Attempting to add a widget with type gtkmm__GtkHBox to a gtkmm__GtkDialog, but as a GtkBin subclass a gtkmm__GtkDialog can only contain one widget at a time; it already contains a widget of type GtkVBox

and the dialog is empty, tiny sized, not modal, and jumps up in the corner of the screen...