diff --git a/PortfolioManager/Cache/SymbolCache.cs b/PortfolioManager/Cache/SymbolCache.cs
index 878f961..f6c584c 100644
--- a/PortfolioManager/Cache/SymbolCache.cs
+++ b/PortfolioManager/Cache/SymbolCache.cs
@@ -36,31 +36,39 @@ namespace PortfolioManager.Cache
         symbolCache=new List<string>();
       }
     }
+
     public void Dispose()
     {
       lock(thisLock)
       {
-	    if(null==symbolCacheInstance || false==threadRun)return;
+			  if(null==symbolCacheInstance || false==threadRun)return;
         threadRun=false;
-        if(null!=cacheMonitorThread)
-        {
-          MDTrace.WriteLine(LogLevel.DEBUG,String.Format("[SymbolCache:Dispose]Thread state is {0}.  Joining main thread...",Utility.ThreadStateToString(cacheMonitorThread)));
-          cacheMonitorThread.Join(5000);
-          cacheMonitorThread=null;
-          MDTrace.WriteLine(LogLevel.DEBUG,"[SymbolCache:Dispose] End.");
-        }
         symbolCacheInstance=null;
       }
+      if(null!=cacheMonitorThread)
+      {
+        MDTrace.WriteLine(LogLevel.DEBUG,String.Format("[SymbolCache:Dispose]Thread state is {0}.  Joining main thread...",Utility.ThreadStateToString(cacheMonitorThread)));
+        cacheMonitorThread.Join(5000);
+        cacheMonitorThread=null;
+        MDTrace.WriteLine(LogLevel.DEBUG,"[SymbolCache:Dispose] End.");
+      }
     }
 
     public List<String> GetSymbols()
     {
-      lock(this)
+      lock(thisLock)
       {
-        if(0==symbolCache.Count)symbolCache=PricingDA.GetSymbols();
-        return symbolCache;
+        if(symbolCache.Count>0)return new List<string>(symbolCache);
+      }
+      List<String> symbols = PricingDA.GetSymbols();
+      lock(thisLock)
+      {
+        if(symbolCache.Count>0)return new List<string>(symbolCache);
+        symbolCache=new List<String>(symbols);
+        return new List<string>(symbols);
       }
     }
+
     private void ThreadProc()
     {
       int quantums=0;
@@ -68,13 +76,15 @@ namespace PortfolioManager.Cache
       while(threadRun)
       {
         Thread.Sleep(quantumInterval);
+        if(!threadRun)break;
         quantums+=quantumInterval;
         if(quantums>cacheRefreshAfter)
         {
           quantums=0;
+          List<String> symbols =  PricingDA.GetSymbols();
           lock(thisLock)
           {
-            symbolCache=PricingDA.GetSymbols();
+            symbolCache=new List<string>(symbols);
           }
         }
       }