This.text is not always an option. Try this:

oForm = CREATEOBJECT("Form")
oForm.Autocenter = .T.
oForm.Addobject('combo','_combobox')
oForm.combo.Visible = .T.

oForm.Show()
READ EVENTS

DEFINE CLASS _combobox AS combobox
       Inputmask = "X-X-X"
       Format = "R" 
       PROCEDURE InteractiveChange
                 ACTIVATE SCREEN
                 ?'InteractiveChange fires'
                 ?'THIS.DisplayValue returns: '
                 ??THIS.DisplayValue
                 ?'THIS.Text returns: '
                 ??THIS.Text
       ENDPROC
ENDDEFINE

>>See this message.
>
>Tonis,
>Right. Simple workarounds work :
>

oForm = CREATEOBJECT("Form")
>oForm.Autocenter = .T.
>oForm.Addobject('combo','_combobox')
>oForm.combo.Visible = .T.
>
>oForm.Show()
>Read EVENTS
>
>Define CLASS _combobox AS combobox
>  Procedure InterActiveChange
>  Activate SCREEN
>*!*	                 lnStart=this.selstart
>*!*	                 this.displayvalue=this.text
>*!*	                 this.selstart=lnStart
>  ?'InterActiveChange fires'
>  ?'THIS.Displayvalue returns: ',THIS.Displayvalue
>  ?'THIS.Text returns: ',THIS.Text
>
>Endproc
>Enddefine

Cetin