Make sure that channel is transitioned to the closed state before returning connection to the pool

src/System.ServiceModel.NetFramingBase/src/System/ServiceModel/Channels/TransportDuplexSessionChannel.cs

@@ -17,6 +17,7 @@ internal abstract class TransportDuplexSessionChannel : TransportOutputChannel,
     {
         private bool _isInputSessionClosed;
         private bool _isOutputSessionClosed;
+        private bool _releasingConnection;
         private Uri _localVia;
         private ChannelBinding _channelBindingToken;
 
@@ -290,6 +291,11 @@ protected async Task CloseOutputSessionAsync(TimeSpan timeout)
 
         protected override void OnAbort()
         {
+            if (_releasingConnection)
+            {
+                // We are releasing the connection to the pool.
+                return;
+            }
             ReturnConnectionIfNecessary(true, TimeSpan.Zero);
         }
 
@@ -567,6 +573,9 @@ private void OnOutputSessionClosed(ref TimeoutHelper timeoutHelper)
 
             if (releaseConnection)
             {
+                // Call Abort() to ensure proper channel state before returning the connection to the pool.
+                _releasingConnection = true;
+                Abort();
                 ReturnConnectionIfNecessary(false, timeoutHelper.RemainingTime());
             }
         }

src/System.ServiceModel.Primitives/src/System/ServiceModel/Channels/ServiceChannel.cs

@@ -374,6 +374,7 @@ private void SetupInnerChannelFaultHandler()
             // NullReferenceException in this method or in the OnInnerChannelFaulted method; 
             // because this method accesses this.binder and OnInnerChannelFaulted accesses this.clientRuntime.
             Binder.Channel.Faulted += OnInnerChannelFaulted;
+            Binder.Channel.Closed += OnInnerChannelClosed;
         }
 
         private void BindDuplexCallbacks()
@@ -1169,6 +1170,16 @@ private void OnInnerChannelFaulted(object sender, EventArgs e)
             }
         }
 
+        private void OnInnerChannelClosed(object sender, EventArgs e)
+        {
+            if (HasSession)
+            {
+                DispatchRuntime dispatchRuntime = ClientRuntime.DispatchRuntime;
+            }
+
+            Abort();
+        }
+
         private void AddMessageProperties(Message message, OperationContext context)
         {
             if (_allowOutputBatching)