diff --git a/Source/MQTTnet/Adapter/MqttChannelAdapter.cs b/Source/MQTTnet/Adapter/MqttChannelAdapter.cs
index 4e61733..13e6606 100644
--- a/Source/MQTTnet/Adapter/MqttChannelAdapter.cs
+++ b/Source/MQTTnet/Adapter/MqttChannelAdapter.cs
@@ -150,6 +150,9 @@ namespace MQTTnet.Adapter
 
                 return packet;
             }
+            catch (OperationCanceledException)
+            {
+            }
             catch (Exception exception)
             {
                 if (IsWrappedException(exception))
@@ -237,7 +240,8 @@ namespace MQTTnet.Adapter
         {
             if (exception is IOException && exception.InnerException is SocketException socketException)
             {
-                if (socketException.SocketErrorCode == SocketError.ConnectionAborted)
+                if (socketException.SocketErrorCode == SocketError.ConnectionAborted ||
+                    socketException.SocketErrorCode == SocketError.OperationAborted)
                 {
                     throw new OperationCanceledException();
                 }
diff --git a/Source/MQTTnet/Client/MqttClient.cs b/Source/MQTTnet/Client/MqttClient.cs
index 575cc90..0a408d0 100644
--- a/Source/MQTTnet/Client/MqttClient.cs
+++ b/Source/MQTTnet/Client/MqttClient.cs
@@ -54,12 +54,12 @@ namespace MQTTnet.Client
 
             try
             {
-                _cancellationTokenSource = new CancellationTokenSource();
-                _disconnectReason = new TaskCompletionSource<bool>();
                 _options = options;
                 _packetIdentifierProvider.Reset();
                 _packetDispatcher.Reset();
 
+                _cancellationTokenSource = new CancellationTokenSource();
+                _disconnectReason = new TaskCompletionSource<bool>();
                 _adapter = _adapterFactory.CreateClientAdapter(options, _logger);
 
                 _logger.Verbose($"Trying to connect with server ({_options.ChannelOptions}).");
@@ -87,10 +87,12 @@ namespace MQTTnet.Client
             catch (Exception exception)
             {
                 _logger.Error(exception, "Error while connecting with server.");
+
                 if (_disconnectReason.TrySetException(exception))
                 {
                     await DisconnectInternalAsync(null, exception).ConfigureAwait(false);
                 }
+
                 throw;
             }
         }
@@ -183,7 +185,7 @@ namespace MQTTnet.Client
 
         public void Dispose()
         {
-            _cancellationTokenSource?.Cancel (false);
+            _cancellationTokenSource?.Cancel(false);
             _cancellationTokenSource?.Dispose();
             _cancellationTokenSource = null;
 
@@ -224,9 +226,10 @@ namespace MQTTnet.Client
 
         private async Task DisconnectInternalAsync(Task sender, Exception exception)
         {
-            InitiateDisconnect();
-
             var clientWasConnected = IsConnected;
+
+            InitiateDisconnect();
+            
             IsConnected = false;
 
             try
@@ -247,7 +250,7 @@ namespace MQTTnet.Client
             }
             finally
             {
-                Dispose ();
+                Dispose();
                 _cleanDisconnectInitiated = false;
 
                 _logger.Info("Disconnected.");
@@ -261,16 +264,16 @@ namespace MQTTnet.Client
             {
                 try
                 {
-                    if (_cancellationTokenSource == null || _cancellationTokenSource.IsCancellationRequested)
+                    if (_cancellationTokenSource?.IsCancellationRequested == true)
                     {
                         return;
                     }
 
-                    _cancellationTokenSource.Cancel(false);
+                    _cancellationTokenSource?.Cancel(false);
                 }
-                catch (Exception adapterException)
+                catch (Exception exception)
                 {
-                    _logger.Warning(adapterException, "Error while initiating disconnect.");
+                    _logger.Warning(exception, "Error while initiating disconnect.");
                 }
             }
         }
@@ -377,8 +380,10 @@ namespace MQTTnet.Client
             {
                 while (!cancellationToken.IsCancellationRequested)
                 {
-                    var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero, cancellationToken).ConfigureAwait(false);
-                    if (packet != null)
+                    var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero, cancellationToken)
+                        .ConfigureAwait(false);
+
+                    if (packet != null && !cancellationToken.IsCancellationRequested)
                     {
                         await ProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
                     }
@@ -393,7 +398,6 @@ namespace MQTTnet.Client
 
                 if (exception is OperationCanceledException)
                 {
-                    _logger.Verbose ("MQTT OperationCanceled exception while receiving packets.");
                 }
                 else if (exception is MqttCommunicationException)
                 {
@@ -492,16 +496,20 @@ namespace MQTTnet.Client
 
         private void StartReceivingPackets(CancellationToken cancellationToken)
         {
-            _packetReceiverTask = Task.Run(
+            _packetReceiverTask = Task.Factory.StartNew(
                 () => ReceivePacketsAsync(cancellationToken),
-                cancellationToken);
+                cancellationToken,
+                TaskCreationOptions.LongRunning, 
+                TaskScheduler.Default);
         }
 
         private void StartSendingKeepAliveMessages(CancellationToken cancellationToken)
         {
-            _keepAliveMessageSenderTask = Task.Run(
+            _keepAliveMessageSenderTask = Task.Factory.StartNew(
                 () => SendKeepAliveMessagesAsync(cancellationToken),
-                cancellationToken);
+                cancellationToken,
+                TaskCreationOptions.LongRunning,
+                TaskScheduler.Default);
         }
 
         private void FireApplicationMessageReceivedEvent(MqttPublishPacket publishPacket)
diff --git a/Tests/MQTTnet.Core.Tests/MqttServerTests.cs b/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
index 0c34bde..e4e5b3b 100644
--- a/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
+++ b/Tests/MQTTnet.Core.Tests/MqttServerTests.cs
@@ -8,6 +8,7 @@ using System.Collections.Generic;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Adapter;
 using MQTTnet.Implementations;
 
 namespace MQTTnet.Core.Tests
@@ -552,6 +553,51 @@ namespace MQTTnet.Core.Tests
             Assert.IsTrue(bodyIsMatching);
         }
 
+        [TestMethod]
+        public async Task MqttServer_ConnectionDenied()
+        {
+            var server = new MqttFactory().CreateMqttServer();
+            var client = new MqttFactory().CreateMqttClient();
+
+            try
+            {
+                var options = new MqttServerOptionsBuilder().WithConnectionValidator(context =>
+                {
+                    context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedNotAuthorized;
+                }).Build();
+
+                await server.StartAsync(options);
+
+                
+                var clientOptions = new MqttClientOptionsBuilder()
+                    .WithTcpServer("localhost").Build();
+
+                try
+                {
+                    await client.ConnectAsync(clientOptions);
+                    Assert.Fail("An exception should be raised.");
+                }
+                catch (Exception exception)
+                {
+                    if (exception is MqttConnectingFailedException)
+                    {
+
+                    }
+                    else
+                    {
+                        Assert.Fail("Wrong exception.");
+                    }
+                }
+            }
+            finally
+            {
+                await client.DisconnectAsync();
+                await server.StopAsync();
+                
+                client.Dispose();
+            }
+        }
+
         [TestMethod]
         public async Task MqttServer_SameClientIdConnectDisconnectEventOrder()
         {