diff --git a/Capnp.Net.Runtime.Tests/CapabilityReflectionTests.cs b/Capnp.Net.Runtime.Tests/CapabilityReflectionTests.cs
new file mode 100644
index 0000000..ccc529d
--- /dev/null
+++ b/Capnp.Net.Runtime.Tests/CapabilityReflectionTests.cs
@@ -0,0 +1,30 @@
+using Capnp.Rpc;
+using Capnproto_test.Capnp.Test;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Capnp.Net.Runtime.Tests
+{
+    [TestClass]
+    [TestCategory("Coverage")]
+    public class CapabilityReflectionTests
+    {
+        [TestMethod]
+        public void ValidateCapabilityInterface()
+        {
+            Assert.ThrowsException<ArgumentNullException>(() => CapabilityReflection.ValidateCapabilityInterface(null));
+            CapabilityReflection.ValidateCapabilityInterface(typeof(ITestInterface));
+            Assert.ThrowsException<InvalidCapabilityInterfaceException>(() => CapabilityReflection.ValidateCapabilityInterface(typeof(CapabilityReflectionTests)));
+        }
+
+        [TestMethod]
+        public void IsValidCapabilityInterface()
+        {
+            Assert.ThrowsException<ArgumentNullException>(() => CapabilityReflection.IsValidCapabilityInterface(null));
+            Assert.IsTrue(CapabilityReflection.IsValidCapabilityInterface(typeof(ITestInterface)));
+            Assert.IsFalse(CapabilityReflection.IsValidCapabilityInterface(typeof(CapabilityReflectionTests)));
+        }
+    }
+}
diff --git a/Capnp.Net.Runtime.Tests/EdgeCaseHandling.cs b/Capnp.Net.Runtime.Tests/EdgeCaseHandling.cs
index 0e61fa5..5ec303d 100644
--- a/Capnp.Net.Runtime.Tests/EdgeCaseHandling.cs
+++ b/Capnp.Net.Runtime.Tests/EdgeCaseHandling.cs
@@ -22,14 +22,16 @@ namespace Capnp.Net.Runtime.Tests
         {
             readonly FramePump _fromEnginePump;
             readonly BinaryReader _reader;
+            readonly FrameTracing.RpcFrameTracer _tracer;
 
             public bool Dismissed { get; private set; }
 
             public MemStreamEndpoint()
             {
                 var pipe = new Pipe();
+                _tracer = new FrameTracing.RpcFrameTracer(Console.Out, false);
                 _fromEnginePump = new FramePump(pipe.Writer.AsStream());
-                _fromEnginePump.AttachTracer(new FrameTracing.RpcFrameTracer(Console.Out, false));
+                _fromEnginePump.AttachTracer(_tracer);
                 _reader = new BinaryReader(pipe.Reader.AsStream());
             }
 
@@ -45,7 +47,9 @@ namespace Capnp.Net.Runtime.Tests
 
             public WireFrame ReadNextFrame()
             {
-                return _reader.ReadWireFrame();
+                var frame = _reader.ReadWireFrame();
+                _tracer.TraceFrame(FrameTracing.FrameDirection.Rx, frame);
+                return frame;
             }
         }
 
@@ -1252,5 +1256,31 @@ namespace Capnp.Net.Runtime.Tests
 
             Assert.IsFalse(tester.IsDismissed);
         }
+
+        [TestMethod]
+        public void ReturnToWrongSide1()
+        {
+            var tester = new RpcEngineTester();
+
+            var cap = tester.RealEnd.QueryMain();
+            var proxy = new BareProxy(cap);
+            Assert.IsFalse(proxy.WhenResolved.IsCompleted);
+            uint id = 0;
+
+            tester.Recv(_ => {
+                Assert.AreEqual(Message.WHICH.Bootstrap, _.which);
+                id = _.Bootstrap.QuestionId;
+            });
+            tester.Send(_ => {
+                _.which = Message.WHICH.Return;
+                _.Return.which = Return.WHICH.ResultsSentElsewhere;
+            });
+            tester.Recv(_ => {
+                Assert.AreEqual(Message.WHICH.Finish, _.which);
+            });
+            Assert.IsTrue(proxy.WhenResolved.IsCompleted);
+            Assert.IsTrue(proxy.WhenResolved.IsFaulted);
+            tester.ExpectAbort();
+        }
     }
 }
diff --git a/Capnp.Net.Runtime.Tests/SerializationTests.cs b/Capnp.Net.Runtime.Tests/SerializationTests.cs
index 57874ef..ad40dc2 100644
--- a/Capnp.Net.Runtime.Tests/SerializationTests.cs
+++ b/Capnp.Net.Runtime.Tests/SerializationTests.cs
@@ -723,7 +723,7 @@ namespace Capnp.Net.Runtime.Tests
         [TestMethod]
         public void DynamicSerializerStateSBytes()
         {
-            var expected = new sbyte[] { 1, 2, 3 };
+            var expected = new List<sbyte> { 1, 2, 3 };
 
             var b = MessageBuilder.Create();
             var dss = b.CreateObject<DynamicSerializerState>();
@@ -735,7 +735,7 @@ namespace Capnp.Net.Runtime.Tests
         [TestMethod]
         public void DynamicSerializerStateShorts()
         {
-            var expected = new short[] { 1, 2, 3 };
+            var expected = new List<short> { 1, 2, 3 };
 
             var b = MessageBuilder.Create();
             var dss = b.CreateObject<DynamicSerializerState>();
@@ -759,7 +759,7 @@ namespace Capnp.Net.Runtime.Tests
         [TestMethod]
         public void DynamicSerializerStateInts()
         {
-            var expected = new int[] { 1, 2, 3 };
+            var expected = new List<int> { 1, 2, 3 };
 
             var b = MessageBuilder.Create();
             var dss = b.CreateObject<DynamicSerializerState>();
@@ -783,7 +783,7 @@ namespace Capnp.Net.Runtime.Tests
         [TestMethod]
         public void DynamicSerializerStateLongs()
         {
-            var expected = new long[] { 1, 2, 3 };
+            var expected = new List<long> { 1, 2, 3 };
 
             var b = MessageBuilder.Create();
             var dss = b.CreateObject<DynamicSerializerState>();
diff --git a/Capnp.Net.Runtime/Rpc/PendingQuestion.cs b/Capnp.Net.Runtime/Rpc/PendingQuestion.cs
index f2e5917..97be61a 100644
--- a/Capnp.Net.Runtime/Rpc/PendingQuestion.cs
+++ b/Capnp.Net.Runtime/Rpc/PendingQuestion.cs
@@ -127,6 +127,7 @@ namespace Capnp.Rpc
         }
 
         const string ReturnDespiteTailCallMessage = "Peer sent actual results despite the question was sent as tail call. This was not expected and is a protocol error.";
+        const string UnexpectedTailCallReturnMessage = "Peer sent the results of this questions somewhere else. This was not expected and is a protocol error.";
 
         internal void OnReturn(DeserializerState results)
         {
@@ -138,6 +139,7 @@ namespace Capnp.Rpc
             if (StateFlags.HasFlag(State.TailCall))
             {
                 _tcs.TrySetException(new RpcException(ReturnDespiteTailCallMessage));
+                throw new RpcProtocolErrorException(ReturnDespiteTailCallMessage);
             }
             else
             {
@@ -157,7 +159,8 @@ namespace Capnp.Rpc
 
             if (!StateFlags.HasFlag(State.TailCall))
             {
-                _tcs.TrySetException(new RpcException("Peer sent the results of this questions somewhere else. This was not expected and is a protocol error."));
+                _tcs.TrySetException(new RpcException(UnexpectedTailCallReturnMessage));
+                throw new RpcProtocolErrorException(UnexpectedTailCallReturnMessage);
             }
             else
             {
diff --git a/Capnp.Net.Runtime/Rpc/RpcEngine.cs b/Capnp.Net.Runtime/Rpc/RpcEngine.cs
index 83ee8f7..60cc0ef 100644
--- a/Capnp.Net.Runtime/Rpc/RpcEngine.cs
+++ b/Capnp.Net.Runtime/Rpc/RpcEngine.cs
@@ -238,8 +238,7 @@ namespace Capnp.Rpc
                 lock (_reentrancyBlocker)
                 {
                     if (!_exportTable.TryGetValue(preliminaryId, out var existing) ||
-                        existing.Cap != preliminaryCap ||
-                        existing.RefCount == 0)
+                        existing.Cap != preliminaryCap)
                     {
                         // Resolved too late. Capability was already released.
                         return;
@@ -579,7 +578,7 @@ namespace Capnp.Rpc
                     {
                         foreach (var cap in inParams.Caps)
                         {
-                            cap?.Release();
+                            cap.Release();
                         }
 
                         pendingAnswer = new PendingAnswer(