Controls disappear after tabbing through

Hello,

I have a transparent UserControl

I got that with this code:

Constructor:

SetStyle(ControlStyles.Opaque, true);
SetStyle(ControlStyles.UserPaint, true);
SetStyle(ControlStyles.AllPaintingInWmPaint,true);
SetStyle(ControlStyles.SupportsTransparentBackColor, true);
BackColor = Color.FromArgb(0, 0, 0, 0);

protected override CreateParams CreateParams
{
    get
    {
      CreateParams cp = base.CreateParams;
      cp.ExStyle |= 0x00000020;
      return cp;
    }
}
)

The transparency works great but now the controls (Textboxes and Grid) on the usercontrol disappear. Each one is gone after I tab off of it. They will come back when I move the mouse over them (For the Grid, each cell comes back single) What's happening?

lionee