/// <summary>
/// Raises the <see cref="E:System.Windows.Forms.Control.MouseUp"></see> event.
/// </summary>
/// <param name="e">A <see cref="T:System.Windows.Forms.MouseEventArgs"></see> that contains the event data.</param>
protected override void OnMouseUp(MouseEventArgs e)
{
base.OnMouseUp(e);
columns.MouseUp(e);
}