PositionsOnClosed with ClosePosition

Hi,

I tried to close the position partially with 

ClosePosition(Position position, long volume)

However, when setting the volume its not calling the method below. It just works when closing the position it self.

protected override void OnStart()
{
    Positions.Closed += PositionsClosed;
}
private void PositionsOnClosed(PositionClosedEventArgs args)
{
    var position = args.Position;
    Print("Position closed with {0} profit", position.GrossProfit);
}

Am I missing something? Is there a way of getting a callback of the volume closed?

Thanks