Websharper - issue with POST expecting a JSON body

Main.fs

// Issue decribed here: http://websharper.com/question/82758/post-endpoint-with-a-json-body-cannot-be-reached

namespace HelloWebSharper

open WebSharper.Html.Server
open WebSharper
open WebSharper.Sitelets

module Site =

    type EndPoint =
        | [<EndPoint "GET /get">] Get
        | [<EndPoint "POST /post_query"; Query "query">] PostQuery of query: string
        | [<EndPoint "POST /post_body"; Json "body">] PostBody of body: JsonBody
        | [<EndPoint "POST /post_simple">] PostSimple

    and JsonBody = { test: string; }

    [<Website>]
    let Main =

        let mainWebsite = Application.MultiPage (fun context action ->
            match action with
            | EndPoint.Get -> Content.Json ("Get works!")
            | EndPoint.PostQuery query -> Content.Json ("PostQuery works!")
            | EndPoint.PostBody body -> Content.Json ("PostBody works!")
            | EndPoint.PostSimple -> Content.Json ("PostSimple works!")
        )

        Sitelet.Sum [ mainWebsite ]

// Run the server as a console application using Owin
module SelfHostedServer =

    open global.Owin
    open Microsoft.Owin.Hosting
    open Microsoft.Owin.StaticFiles
    open Microsoft.Owin.FileSystems
    open WebSharper.Owin
    open System
    open System.Collections.Generic
    open System.Threading.Tasks

    type Greeting = { text: string }
    type AppFunc = Func<IDictionary<string, obj>, Task>
    let awaitTask = Async.AwaitIAsyncResult >> Async.Ignore
    
    type Startup() =

        member this.Configuration(app: IAppBuilder) =

//            // Log info about incoming requests to the console
            app.Use(fun environment next ->
                printfn "------ New request ------"
                printfn "  Path: %s" (environment.Request.Path.ToString())
                printfn "  Verb: %s" (environment.Request.Method)
                
                // If we comment the next 3 lines, the POST with body will work!
                use reader = new System.IO.StreamReader(environment.Request.Body)
                let body = reader.ReadToEnd()
                printfn "  Body: %s" (body)

                async { 
                    do! awaitTask <| next.Invoke()
                    printfn "  HTTP Status code: %i" environment.Response.StatusCode

                    if environment.Response.StatusCode <> 200 then 
                        use writer = new System.IO.StreamWriter(environment.Response.Body)
                        writer.WriteLine("an error occurred!")
                        writer.Flush |> ignore

                } |> Async.StartAsTask :> Task) |> ignore

            // Load our site
            app.UseStaticFiles(
                    StaticFileOptions(
                        FileSystem = PhysicalFileSystem("..")))
                .UseSitelet("..", Site.Main)
            |> ignore

    [<EntryPoint>]
    let main argv = 
        let uri = "http://localhost:9000"
        use app = WebApp.Start<Startup>(uri)
        printfn "Serving %s" uri
        Console.ReadKey() |> ignore
        printfn "Stopping %s" uri
        0