Code

class MyBehavior : MindFusion.FlowChartX.Behaviors.CreateArrowBehavior
{
 public MyBehavior(FlowChart fc) : base(fc)
 {
 }

 public override InteractionState StartDraw(PointF point)
 {
   InteractionState ist = base.StartDraw(point);

   if (ist.Action == Action.Create && ist.CurrentObject is Arrow)
   {
     Node node = fc.GetNodeAt(point, true, false);
     if (node != null)
     {
       if (node.AnchorPattern == null)
         return ist;

       foreach (AnchorPoint p in node.AnchorPattern.Points)
      {
       RectangleF r = node.BoundingRect;
       PointF appos = new PointF(r.X + r.Width * p.X / 100, r.Y + r.Height * p.Y / 100);

       if (p.AllowOutgoing && Math.Abs(point.X - appos.X) < 3 && Math.Abs(point.Y - appos.Y) < 3)
        return ist;
      }

      return null;
     }
   }

   return ist;
 }
}