Problem with datepick control and bchange

[Silvio.Falconi]

On a dialog I have this control

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@  22,140 DTPICKER oDtpLast VAR dLast SIZE 80,12 PIXEL OF oFolder:aDialogs[1] ;
      PICTURE "ddd dd mmm yyyy"  UPDATE ;
      ON CHANGE (deletefromCombo(oBrowse,aGetTotali) ,oBtnSearch:enable() )

the function deletefromCombo(oBrowse,aGetTotali) delete all rows on the oBrowse , but this operation must be made only if the date dLast is changed by operator

but it is processed before of all

why ?

I would like that function to be called only and exclusively if the operator changes the date
why does fivewin call that function even though the operator hasn't changed anything?

[Silvio.Falconi]

now I tried
ON CHANGE (IIF( oDtpLast:Changed(),deletefromCombo(oBrowse,aGetTotali),), oBtnSearch:enable() )

but the application is crashed