C#

using UiLibrary;
namespace DirectApp
{
  static class Program
  {
    [STAThread]
    static void Main ()
    {
      Application.EnableVisualStyles ();
      Application.SetCompatibleTextRenderingDefault (false);
      Application.Run (new Form1 ());
} } }

namespace IndirectApp
{
  public partial class DummyFormToLaunchTheRealUI
  {
    public DummyFormToLaunchTheRealUI () { InitializeComponent (); }

    private void button1_Click (object sender, EventArgs e)
    {
      Assembly abs = Assembly.LoadFile (@"C:\temp\tester\UiLibrary\bin\debug\UiLibrary.dll");
      Type startType = abs.GetType ("UiLibrary.Startup", true);
      object startLib = startType.InvokeMember ("", BindingFlags.CreateInstance, null, null, new object[0]);
      startType.InvokeMember ("Run", BindingFlags.InvokeMethod, null, startLib, new object[0]);
} } }

namespace UiLibrary
{
  public class Startup
  {
    public void Run ()
    {
      Thread runThread = new Thread (new ThreadStart (ActualWork));
      runThread.Start ();
    }

    private void ActualWork ()
    {
      Form1 f = new Form1 ();
      f.ShowDialog ();
    }
  }

  public partial class Form1 : Form
  {
    public Form1 () { InitializeComponent (); }

    private void button1_click (object sender, EventArgs e)
    {
      OpenFileDialog ofd = new OpenFileDialog ();
      // this field always correct
      ofd.InitialDirectory = Environment.ExpandEnvironmentVariables (@"%USERPROFILE%\Downloads");
      // doesn't change if call ShowDialog with no paramters
      ofd.ShowDialog (this);
} } }