DatagridView moving strange (or how to block your application)

Attrached a sample project (with basically 20 lines of code) and a short 15 seconds video with program running and problem happening:

– create a form with one exit button and a datagridView, and open with  ShowDialog. No auto-size, nothing additional. If you click inside the table and after that click outside the table (near the button), the datagridview is displayed on all windows, the button is probably hidden, so no way to get out.

I dont’t want a way to get out (it’s pretty trivial to do that), but what happens to datagrid covering everything?

private void button1_Click(object sender, EventArgs e)
{
Form f = new Form();
f.Size = new Size(600, 400);
f.StartPosition = FormStartPosition.CenterScreen;
f.FormBorderStyle = FormBorderStyle.FixedToolWindow;
f.Text = “test”;
f.ControlBox = false;

Button b = new Button();
b.Text = “Exit”;
b.Width = 100; b.Height = 25;
b.Click += delegate { f.Close(); };
b.Left = f.Width / 2 – b.Width / 2;
b.Top = 5;// f.Height – b.Height – 5;
f.Controls.Add(b);

Wisej.Web.DataGridView dg = new Wisej.Web.DataGridView();
dg.Width = f.Width – 10;
dg.Height = f.Height – b.Height – 10;
dg.Left = 5; dg.Top = b.Height + 10;
f.Controls.Add(dg);
f.ShowDialog();
}