ListBox.OnCurrentIndexChanged in GroupBox ineffective

[Coder]

when I put ListBox in GroupBox ，OnCurrentIndexChanged and OnItemActivated is Ineffective。

I modified the listbox example, just like this:

                           GroupBox{
				Layout: VBox{},
				Children: []Widget{
					ListBox{
						AssignTo:              &mw.lb,
						Model:                 mw.model,
						OnCurrentIndexChanged: mw.nglb_CurrentIndexChanged,
						OnItemActivated:       mw.nglb_ItemActivated,
					},
					TextEdit{
						AssignTo: &mw.te,
						ReadOnly: true,
					},
				},
		

[Coder]

I put HSplitter in GroupBox， and the methods are useful.
I still want to know the reason.
Forgive me