GtkComboBox needs "activates-default" property
Submitted by Sven Neumann
GtkComboBox reacts to the Enter key, just like a GtkEntry. This means that if a dialog has a GtkComboBox as its first focus widget, then the dialog's default action cannot any longer be activated by pressing the Enter key. GtkEntry has an "activates-default" property that allows an application developer to change the behaviour so that the entry calls gtk_window_activate_default() on the window containing the entry in the default handler for the "activate" signal. Such a property should also exist on a GtkComboBox.
See bug #380848 for an example of this problem.