[gtkmm] How can I do this with radio menu items ?

["Nad" <enidan971 free fr>]

Hello all,

I've got a menu with 4 radio menu items (Gtk::RadioMenuItem) for users to
choose between 3 sizes or a custom size.
But my application can also load a saved state, so i've got a method to
select the good item in the menu with CheckMenuItem::set_active().

What doesn't works it that when one item is already selected, it seems that
"activate" signal is not re-emitted when the user clicks it.
So I can't have the wanted behaviour for my "custom size" item.

Is there a solution ?