My Trailing stop is not working well

Hello,
my trailing stop does not fix it.
 
example:
when my order at 0.32lots opens to bull and it goes up my trailing stop also
goes up and it's good but it also goes down when it should not.

all this in the strategy tester,
test it on the week 2011/01/31 at the GBPUSD and you'll understand


void Trailing()
  {
   double tstart=0; double tstop=0; double tstep=0; double SL=0;
   
   tstart=TrailingStart*10; tstop=TrailingStop*10; tstep=TrailingStep*10;

   for(int i=0; i<OrdersTotal(); i++)
      if(OrderSelect(i,SELECT_BY_POS,MODE_TRADES))
         if(OrderSymbol()==Symbol() && OrderMagicNumber()==magic_5)
           {
            if(OrderType()==OP_BUY)
              {
               if(Bid-OrderOpenPrice()>=tstart*_Point)
                 {
                  if(OrderStopLoss()<Bid-(tstop+tstep)*_Point || OrderStopLoss()==0)
                  SL=NormalizeDouble(Bid-(tstop*_Point),_Digits);
                  bool modify=OrderModify(OrderTicket(),OrderOpenPrice(),SL,OrderTakeProfit(),0,clrNONE);
                 }
              }

            if(OrderType()==OP_SELL)
              {
               if(OrderOpenPrice()-Ask>=tstart*_Point)
                 {
                  if(OrderStopLoss()>Ask+(tstop+tstep)*_Point || OrderStopLoss()==0)
                  SL=NormalizeDouble(Ask+(tstop*_Point),_Digits);
                  bool modify1=OrderModify(OrderTicket(),OrderOpenPrice(),SL,OrderTakeProfit(),0,clrNONE);
                 }
              }
           }
  }