Added some code comments and did a check for redirects (returns null if this is the case)

src/Umbraco.Web/Mvc/RenderRouteHandler.cs

@@ -270,6 +270,12 @@ namespace Umbraco.Web.Mvc
 			if (!publishedContentRequest.HasTemplate && !routeDef.HasHijackedRoute)
 			{
 				var handler = publishedContentRequest.ProcessNoTemplateInMvc(requestContext.HttpContext);
+				//though this code should never execute if the ProcessNoTemplateInMvc method redirects, it seems that we should check it
+				//and return null, this could be required for unit testing as well
+				if (publishedContentRequest.IsRedirect)
+				{
+					return null;
+				}
 
 				// if it's not null it can be either the PublishedContentNotFoundHandler (no document was
 				// found to handle 404, or document with no template was found) or the WebForms handler 

src/Umbraco.Web/Routing/PublishedContentRequest.cs

@@ -32,7 +32,6 @@ namespace Umbraco.Web.Routing
 		/// </summary>
 		/// <param name="httpContext"></param>
 		/// <param name="umbracoContext"></param>
-		/// <param name="uri"></param>
 		/// <param name="onSuccess"></param>
 		internal void ProcessRequest(HttpContextBase httpContext, UmbracoContext umbracoContext, Action<PublishedContentRequest> onSuccess)
 		{
@@ -107,6 +106,13 @@ namespace Umbraco.Web.Routing
 				onSuccess(this);
 		}
 
+		/// <summary>
+		/// After execution is handed off to MVC, we can finally check if the request has: No Template assigned and also the 
+		/// route is not hijacked. When this occurs, we need to send the routing back through the builder to check for 
+		/// not found handlers.
+		/// </summary>
+		/// <param name="httpContext"></param>
+		/// <returns></returns>
 		internal IHttpHandler ProcessNoTemplateInMvc(HttpContextBase httpContext)
 		{
 			var content = this.PublishedContent;
@@ -117,7 +123,10 @@ namespace Umbraco.Web.Routing
 
 			// redirect if it has been flagged
 			if (this.IsRedirect)
+			{
 				httpContext.Response.Redirect(this.RedirectUrl, true);
+			}
+				
 
 			// here .Is404 _has_ to be true
 			httpContext.Response.StatusCode = 404;

src/Umbraco.Web/Routing/PublishedContentRequestBuilder.cs

@@ -174,7 +174,10 @@ namespace Umbraco.Web.Routing
 		/// <summary>
 		/// Performs the document resolution second pass.
 		/// </summary>
-		/// <remarks>The second pass consists in handling "not found", internal redirects, access validation, and template.</remarks>
+		/// <remarks>
+		/// The second pass consists in handling "not found", internal redirects, access validation, and template.
+		/// TODO: Rename this method accordingly .... but to what?
+		/// </remarks>
 		internal void LookupDocument2()
 		{
 			const string tracePrefix = "LookupDocument2: ";

src/Umbraco.Web/UmbracoModule.cs

@@ -104,7 +104,8 @@ namespace Umbraco.Web
 			// instanciate a request a process
 			// important to use CleanedUmbracoUrl - lowercase path-only version of the current url
 			var docreq = new PublishedContentRequest(umbracoContext.CleanedUmbracoUrl, umbracoContext.RoutingContext);
-			docreq.ProcessRequest(httpContext, umbracoContext, docreq2 => RewriteToUmbracoHandler(HttpContext.Current, uri.Query, docreq2.RenderingEngine));
+			docreq.ProcessRequest(httpContext, umbracoContext, 
+				docreq2 => RewriteToUmbracoHandler(HttpContext.Current, uri.Query, docreq2.RenderingEngine));
 		}
 
 		/// <summary>