Leak in Mono WinForms

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

static class Program
{
    static Form frm = new Form();

    [STAThread]
    static void Main()
    {
        Timer tmr = new Timer() { Enabled = true };
        tmr.Tick += new EventHandler(tmr_Tick);
        Application.Run(frm);
    }

    static void tmr_Tick(object sender, EventArgs e)
    {
        frm.Controls.Clear(); // <- These controls don't seem to get collected.
        frm.Controls.Add(new Control() { BackgroundImage = new Bitmap(1024, 768) });
    }
}