Deleting an item using Gtk::Menu_Helpers::MenuList::insert() or 
Gtk::Menu_Helpers::MenuList::remove() does not completely remove it.
The item is still available through its keyboard shortcut.

Example code:

#include <gtkmm.h>
#include <iostream>

class TestWindow : public Gtk::Window
{
public:
    TestWindow();

private:
    Gtk::VBox windowVBox;
    Gtk::MenuBar menuBar;
    Gtk::Menu menu_Test1;
    Gtk::Menu menu_Test2;
    
    void delete_with_erase_test();
    void delete_with_remove_test();
};

TestWindow::TestWindow()
{
    set_title("MenuList erase() and remove() bug");
    set_resizable(false);
    set_border_width(5);

  	menu_Test1.items().push_back(Gtk::Menu_Helpers::MenuElem("Delete 
this using erase()",  Gtk::Menu::AccelKey("<control>e"), SigC::slot(*this, 
&TestWindow::delete_with_erase_test)));
    menu_Test1.items().push_back(Gtk::Menu_Helpers::SeparatorElem());
    menu_Test1.items().push_back(Gtk::Menu_Helpers::MenuElem("Quit",  
SigC::slot(*this, &Gtk::Widget::hide)));

  	menu_Test2.items().push_back(Gtk::Menu_Helpers::MenuElem("Delete 
this using remove()",  Gtk::Menu::AccelKey("<control>r"), SigC::slot
(*this, &TestWindow::delete_with_remove_test)));
    menu_Test2.items().push_back(Gtk::Menu_Helpers::SeparatorElem());
    menu_Test2.items().push_back(Gtk::Menu_Helpers::MenuElem("Quit",  
SigC::slot(*this, &Gtk::Widget::hide)));

    menuBar.items().push_back(Gtk::Menu_Helpers::MenuElem("Test 1", 
menu_Test1));
    menuBar.items().push_back(Gtk::Menu_Helpers::MenuElem("Test 2", 
menu_Test2));

    windowVBox.pack_start(menuBar);
    add(windowVBox);
    show_all();
}

void TestWindow::delete_with_erase_test()
{
    Gtk::Menu_Helpers::MenuList::iterator i = menu_Test1.items().begin();
    menu_Test1.items().erase(i);
    std::cout << "Test 1 > 'Delete this using erase()' deleted." << 
std::endl;
    std::cout << "Bug: try to press Ctrl+e" << std::endl;
}

void TestWindow::delete_with_remove_test()
{
    menu_Test2.items().remove(menu_Test2.items()[0]);
    std::cout << "Test 2 > 'Delete this using remove()' deleted." << 
std::endl;
    std::cout << "Bug: try to press Ctrl+r" << std::endl;
}

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

    TestWindow testWindow;
    
    Gtk::Main::run(testWindow);
    
    return 0;
}