How to render input elements inside form elements

Question

Antaris RazorEngine v3.9.3 is used in ASP.NET MVC4 controller to create form element. In result html input elements are rendered outside form element. For example

@using (Html.BeginForm("Test", "Upload"))
{
<input type="file" />
<input type="submit"/>
}

produces

<form action="/Upload/Test" method="post"></form>
<input type="file" />
<input type="submit"/>

while correct result should be

<form action="/Upload/Test" method="post">
<input type="file" />
<input type="submit"/>
</form>

RenderScript returns only input elements. <form action="/Upload/Test" method="post"> is written to output directly. It looks like BeginForm() writes directly to view and Razorengine does not capture its output.

How to fix this ?

View:

        @Model.RenderScript()

Model:

public IHtmlString RenderScript() {
    var config = new TemplateServiceConfiguration();
    config.BaseTemplateType = typeof(HtmlTemplateBase<>);
    config.Namespaces = new HashSet<string>(new string[] {
                    "System",
                    "System.Collections",
                    "System.Collections.Generic",
                    "System.Globalization",
                    "System.Linq",
                    "System.Web",
                    "System.Web.Mvc",
                    "System.Web.Mvc.Html"
                });
    razor = RazorEngineService.Create(config);
    // In real application colModel is retrieved from database
    var colModel=@"
    @using (Html.BeginForm(""Test"", ""Upload""))
    {
    <input type='file' />
    <input type='submit'/>
    }
    ";
    string res = razor.RunCompile(colmodel, colmodel, typeof(object), new object());
    return MvcHtmlString.Create(res);
}

Template base class:

using RazorEngine.Templating;
using RazorEngine.Text;
using System;
using System.IO;
using System.Web;
using System.Web.Mvc;
using System.Web.WebPages;

public class HtmlTemplateBase<T> : TemplateBase<T>, IViewDataContainer
{
    // http://stackoverflow.com/questions/8561164/razorengine-issues-with-html
    HtmlHelper<T> helper = null;
    ViewDataDictionary viewdata = null;

    public HtmlHelper<T> Html
    {
        get
        { 

            // https://github.com/Antaris/RazorEngine/issues/150
             if (helper == null)
            {
                var p = WebPageContext.Current;
                var wvp = p.Page as WebViewPage;
                var context = wvp != null ? wvp.ViewContext : null;

                context.Writer = this.CurrentWriter;

                helper = new HtmlHelper<T>(context, this);
            }

            return helper;
        }
    }


    public ViewDataDictionary ViewData
    {
        get
        {
            if (viewdata == null)
            {
                viewdata = new ViewDataDictionary();
                viewdata.TemplateInfo = new TemplateInfo() { HtmlFieldPrefix = string.Empty };

                if (this.Model != null)
                {
                    viewdata.Model = Model;
                }
            }
            return viewdata;
        }
        set
        {
            viewdata = value;
        }
    }

    public override void WriteTo(TextWriter writer, object value)
    {
        if (writer == null)
            throw new ArgumentNullException("writer");

        if (value == null) return;
        //try to cast to RazorEngine IEncodedString
        var encodedString = value as IEncodedString;
        if (encodedString != null)
        {
            writer.Write(encodedString);
        }
        else
        {
            var htmlString = value as IHtmlString;
            if (htmlString != null) writer.Write(htmlString.ToHtmlString());
            else
            {
                encodedString = TemplateService.EncodedStringFactory.CreateEncodedString(value);
                writer.Write(encodedString);
            }

        }
    }
}

Posted also in https://github.com/Antaris/RazorEngine/issues/443