diff --git a/shadowsocks-csharp/Controller/Service/AvailabilityStatistics.cs b/shadowsocks-csharp/Controller/Service/AvailabilityStatistics.cs
index 790f5d1b..af039b18 100644
--- a/shadowsocks-csharp/Controller/Service/AvailabilityStatistics.cs
+++ b/shadowsocks-csharp/Controller/Service/AvailabilityStatistics.cs
@@ -196,7 +196,12 @@ namespace Shadowsocks.Controller
                 _inboundSpeedRecords.TryGetValue(id, out inboundSpeedRecords);
                 _outboundSpeedRecords.TryGetValue(id, out outboundSpeedRecords);
                 _latencyRecords.TryGetValue(id, out latencyRecords);
-                records.Add(id, new StatisticsRecord(id, inboundSpeedRecords, outboundSpeedRecords, latencyRecords));
+                StatisticsRecord record = new StatisticsRecord(id, inboundSpeedRecords, outboundSpeedRecords, latencyRecords);
+                /* duplicate server identifier */
+                if (records.ContainsKey(id))
+                    records[id] = record;
+                else
+                    records.Add(id, record);
             }
 
             if (Config.Ping)
diff --git a/shadowsocks-csharp/Controller/Service/PolipoRunner.cs b/shadowsocks-csharp/Controller/Service/PolipoRunner.cs
index f824c2e5..1c0efcdd 100644
--- a/shadowsocks-csharp/Controller/Service/PolipoRunner.cs
+++ b/shadowsocks-csharp/Controller/Service/PolipoRunner.cs
@@ -49,8 +49,13 @@ namespace Shadowsocks.Controller
                 {
                     try
                     {
-                        p.Kill();
-                        p.WaitForExit();
+                        p.CloseMainWindow();
+                        p.WaitForExit(100);
+                        if (!p.HasExited)
+                        {
+                            p.Kill();
+                            p.WaitForExit();
+                        }
                     }
                     catch (Exception e)
                     {