Custom-indicator-s-value-does-not-change

I am trying to implement WillVal indicator. It seems to work, but there is one problem. When I change benchmark symbol in the parameters, the indicator value does not change. Why can this be?

CODE:
using WealthLab.Core;
using System;
using System.Drawing;
using WealthLab.Indicators;

namespace WealthLab.MyIndicators
{
   public class WillVal : IndicatorBase
   {
      //parameterless constructor
      public WillVal() : base()
      {
         OverboughtLevel = 85;
         OversoldLevel = 15;
      }

      //for code based construction
      public WillVal(TimeSeries source, String benchmark, Int32 ema1, Int32 ema2, Int32 period)
         : base()
      {
         Parameters[0].Value = source;
         Parameters[1].Value = benchmark;
         Parameters[2].Value = ema1;
         Parameters[3].Value = ema2;
         Parameters[4].Value = period;
         OverboughtLevel = 85;
         OversoldLevel = 15;
         Populate();
      }

      //static Series method
      public static WillVal Series(TimeSeries source, String benchmark, Int32 ema1, Int32 ema2, Int32 period)
      {
         return new WillVal(source, benchmark, ema1, ema2, period);
      }

      //name
      public override string Name
      {
         get
         {
            return "Will Val";
         }
      }

      //abbreviation
      public override string Abbreviation
      {
         get
         {
            return "WillVal";
         }
      }

      //description
      public override string HelpDescription
      {
         get
         {
            return "Larry William's WillVal. Benchmark TLT, GLD, UUP.";
         }
      }

      //price pane
      public override string PaneTag
      {
         get
         {
            return "WillVal";
         }
      }

      //default color
      public override WLColor DefaultColor
      {
         get
         {
            return WLColor.Navy;
         }
      }

      //default plot style
      public override PlotStyle DefaultPlotStyle
      {
         get
         {
            return PlotStyle.Oscillator;
         }
      }

      //populate
      public override void Populate()
      {
         TimeSeries source = Parameters[0].AsTimeSeries;
         String benchmark = Parameters[1].AsString;
         Int32 ema1 = Parameters[2].AsInt;
         Int32 ema2 = Parameters[3].AsInt;
         Int32 period = Parameters[4].AsInt;

         DateTimes = source.DateTimes;

         if (period <= 0 || ema1 <= 0 || ema2 <= 0 || benchmark == "")
            return;

         TimeSeries price = new TimeSeries(DateTimes);
         TimeSeries value = new TimeSeries(DateTimes);
         TimeSeries wv = new TimeSeries(DateTimes);

         BarHistory bBenchmark = WLHost.Instance.GetHistory(benchmark, source.DetermineScale(), DateTime.MinValue, DateTime.MaxValue, 0, null);
         TimeSeries bPrice = TimeSeriesSynchronizer.Synchronize(bBenchmark.Close, source);

         TimeSeries ma1 = EMA.Series(source, ema1);
         TimeSeries ma2 = EMA.Series(source, ema2);

         price = bPrice / source;

         value = ma1 - ma2;

         // Calculate WV series
         for (int i = source.FirstValidIndex; i < source.Count; i++)
         {
            int start = Math.Max(0, i - period + 1);
            double min = value[start];
            double max = value[start];

            for (int j = start; j <= i; j++)
            {
               if (value[j] < min) min = value[j];
               if (value[j] > max) max = value[j];
            }

            if (max != min)
               Values[i] = 100.0 * (value[i] - min) / (max - min);
            else
               Values[i] = double.NaN;
         }
      }

      //generate parameters
      protected override void GenerateParameters()
      {
         AddParameter("Source", ParameterType.TimeSeries, PriceComponent.Close);
         AddParameter("Benchmark", ParameterType.String, "GLD");
         AddParameter("EMA1", ParameterType.Int32, 2);
         AddParameter("EMA2", ParameterType.Int32, 22);
         AddParameter("Period", ParameterType.Int32, 65);
      }
   }
}