I ran your code and I don't undestand what you are trying to show me. With the checkbox value .T., nothing changes, with it .F., then it just works and changes the value in the first column. What are you trying to show?

>With duplicated Values every Value/ControlSource Refresh
>set ListIndex to the first match row
>
>

>PUBLIC oform1
>
>oform1=NEWOBJECT("form1")
>oform1.Show
>
>DEFINE CLASS form1 AS form
>
>
>	Top = 0
>	Left = 0
>	Height = 250
>	Width = 453
>	DoCreate = .T.
>	Caption = "Form1"
>	Name = "form1"
>
>
>	ADD OBJECT combo1 AS combobox WITH ;
>		BoundColumn = 2, ;
>		ColumnCount = 2, ;
>		RowSourceType = 5, ;
>		Height = 24, ;
>		Left = 96, ;
>		Style = 2, ;
>		Top = 60, ;
>		Width = 156, ;
>		BoundTo = .T., ;
>		Name = "Combo1"
>
>
>	ADD OBJECT text1 AS textbox WITH ;
>		ControlSource = "thisform.Combo1.Value", ;
>		Height = 23, ;
>		InputMask = "99999999", ;
>		Left = 264, ;
>		Top = 60, ;
>		Width = 156, ;
>		Name = "Text1"
>
>
>	ADD OBJECT check1 AS checkbox WITH ;
>		Top = 24, ;
>		Left = 96, ;
>		Height = 17, ;
>		Width = 138, ;
>		AutoSize = .T., ;
>		Alignment = 0, ;
>		Caption = "Rewrite Combo Value", ;
>		Value = .T., ;
>		Name = "Check1"
>
>
>	PROCEDURE combo1.Valid
>		IF thisform.Check1.Value
>			this.Value = this.Value
>		ENDIF
>		thisform.Text1.Refresh
>	ENDPROC
>
>
>	PROCEDURE combo1.Init
>		ADDPROPERTY(this,"aItems[256,2]")
>		FOR j=1 TO ALEN(this.aItems,1)
>			This.aItems[m.j,1]="Items"+STR(m.j)
>			This.aItems[m.j,2]=34
>		NEXT
>		this.RowSource = "m.this.aItems"
>		this.Value = 34
>	ENDPROC
>
>
>ENDDEFINE
>