为什么切换窗体的可见性会禁用KeyDown事件？

Panels

this.Visible = false;

this.Visible = true;

 for (int i = 0; i < Size; i++)
        {
            for (int j = 0; j < Size; j++)
            {
                _panel = new Panel();
                _panel.Location = new Point((i * _panel.Size.Width) + ((i + 1) * _border), (j * _panel.Size.Height) + ((j + 1) * _border));                    
                this.Controls.Add(_panel);
            }
        }

KeyDown

this.SuspendLayout();

// Do all the resizing here.

this.ResumeLayout();

this.Visible

style=\"display:none;