Reproducing F# intellisense bug when opening C# namespace with extension methods containing unreferencedtypes

Extensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CsharpProjWithExt
{
    public static class Extensions
    {
        /// <summary>
        ///  An extension method that references "System.Windows.Forms" assembly.
        /// </summary>
        /// <param name="form"></param>
        /// <returns></returns>
        public static string FormToString(this System.Windows.Forms.Form form)
        {
            return form.ToString();
        }
    }
}

Program.fs

open CsharpProjWithExt

[<EntryPoint>]
let main argv = 

    let dir = new System.IO.DirectoryInfo("C:\temp")

    // Intellisense fails when dotting into "dir" fails once "CsharpProjWithExt" is opened.
    // Commenting out the open statement (or commenting out the extension method) restores intellisense.
    let parentName = dir.Parent.FullName

    0