using System.Windows.Forms;
using System;
using System.Drawing;

public class FormTest : System.Windows.Forms.Form {
public FormTest() {
Button b = new  Button();
b.Left = 20;
b.Top = 20;
b.Text = "Click me";
b.Click += new System.EventHandler(ButtonClicked);
Controls.Add(b);
Closed += new System.EventHandler(FormClosed);
}

public void ButtonClicked(object sender, EventArgs e) {
FormTest f = new FormTest();
f.Visible = true;
f.DesktopLocation = DesktopLocation; should open new form at same position
Visible = false;
}

public void FormClosed(object sender, EventArgs e) {
Application.Exit();
}

static void Main() {
Application.Run(new FormTest());
}
}

"set" sets the corner of the outer border (including the border given by the window manager), but "get" returns the corner of the inner window (without the border drawn by the window manager).