This is not a bug. This happens becuase you bind the control to a form property. IntreactiveChange not change the value of that property, this will be happens after Valid. But refreshing the form you rollback the value of the spinner to value of
thisform.nEffe

If you change:

PROCEDURE spinner1.InteractiveChange
        thisform.nEffe = this.Value
	thisform.refresh()
ENDPROC

all will works as you expect. I not tested furter what happens with validation.

>This piece of code demonstrates a spinner that refuses to increase or decrease. The crucial part appears to be the instruction to refresh the form in the interactivechange method.
>
>Who has a clue? Is it a bug? Or am I the one who is doing something really stupid here.
>
>

local ox
>ox = createobject( 'form1' )
>ox.visible = .t.
>read events
>
>DEFINE CLASS form1 AS form

>
>	DoCreate = .T.
>	Caption = "Form1"
>	nEffe = 0
>	Name = "Form1"
>
>	ADD OBJECT spinner1 AS spinner WITH ;
>		Height = 24, ;
>		Left = 198, ;
>		Top = 72, ;
>		Width = 120, ;
>		ControlSource = "thisform.nEffe", ;
>		Name = "Spinner1"
>
>	PROCEDURE spinner1.InteractiveChange
>		thisform.refresh()
>	ENDPROC
>
>	procedure destroy
>		clear events
>	endproc
>
>ENDDEFINE