combo box in dialog did not work, not mouse selctable, lots of Gdk-CRITICAL messages on console output

["Klaus Rudolph" <lts-rudolph gmx de>]

Hi again,

I tried to get a combo box to work in a dialog window. But the behavior is strange. The following things will 
not work:

After the dialog window opens ( after pressing the do button in my example code ) you can open the combo box 
list with a mouse click. But it is not possible to select an item in the list with the mouse! If you change 
the selected entry with the space bar and cursor the console gives an endless list of messages:
"(go:9768): Gdk-CRITICAL **: gdk_window_get_device_position_double: assertion 'GDK_IS_DEVICE (device)' failed"

If I add my combo box to the main window it seems to work normally. Maybe the code is broken in general, but 
if the combo box runs from main window I can no see any misbehavior.

The following code is complete to compile and run.

#include <iostream>
#include <gtkmm.h>
#include <vector>
using namespace std;

Gtk::Window* winptr;

class MyComboBox: public Gtk::ComboBox
{   
    private:
        class ModelColumns : public Gtk::TreeModel::ColumnRecord
    {   
        public:
            ModelColumns()
            {   
                add(m_col_name);
            }
            
            Gtk::TreeModelColumn<Glib::ustring> m_col_name;
    };
        
        ModelColumns m_Columns;
        Glib::RefPtr<Gtk::ListStore> m_refTreeModel;
    
    public:
        MyComboBox(const vector<const char*>& vec, unsigned int startVal)
        {   
            m_refTreeModel = Gtk::ListStore::create(m_Columns);
            set_model(m_refTreeModel);

            
            for ( auto s: vec)
            {   
                Gtk::TreeModel::Row row = *(m_refTreeModel->append());
                row[m_Columns.m_col_name] = s;
            }
            
            pack_start(m_Columns.m_col_name);
            set_active( startVal );
        }
};

void CreateDialog()
{
    std::cout << "Do" << std::endl;
    enum KNOPF
    {
        OK,
        CANCEL
    };

    Gtk::Dialog dialog("Konfiguriere", *winptr, false );

    Gtk::Box* box = dialog.get_vbox();
    MyComboBox cb({{"Eins","Zwei","Drei"}},0);

    box->add( cb );
    dialog.add_button( Gtk::Stock::OK, OK);
    dialog.add_button( Gtk::Stock::CANCEL, CANCEL);
    dialog.set_default_response( CANCEL );

    dialog.show_all_children();

    int ret = dialog.run();
}

int main(int argc, char *argv[])
{
    Gtk::Main kit(argc, argv);

    Gtk::Window win;
    winptr=&win;

    Gtk::Button button("Do");
    button.signal_clicked().connect(sigc::ptr_fun(&CreateDialog));
    win.add(button);
    win.show_all_children();
    Gtk::Main::run(win);
}