I think this behavior is correct since the .Value property isn't being explicitly changed. But try this in the LostFocus()

THIS.Value= THIS.Value

>I tested a new a simple object using the assign method. What I wanted was to have the background colour of the textbox change if the value was changed from the original value. I created a subclassed textbox and added a startingvalue property to use as a reference.
>
>Here is the code for Value_assign method of the textbox subclass:
>
>LPARAMETER vNewval
>
>IF ALLTRIM(vNewval) <> ALLTRIM(this.startvalue)
> this.backcolor = RGB(227, 0, 0)
>ENDIF
>
>THIS.Value = m.vNewVal
>
>Really simple. When I assigned the initial value in the init of a form that had this textbox (first by setting the startvalue and then the textbox value so they would be the same, the assign method fired. However, it only fires if the change to the value occurs within code. If I change the value in the textbox field then the assign method does not fire. What I did to get the behaviour I wanted was add
>this.value_assign(this.value) into the valid clause of the textbox so default valid behaviour is to call the assign method.
>
>Is this the behaviour to expect? That is, the assign method only fires when a textbox receives a new value from code and not during data entry?