Scratch the last respones to you. I found out where to hook the event.
The problem is that at the point of ItemDataBound, the height of the panel is still the default size, it hasn't been changed. so the function:
private void detail_ItemDataBound(object sender, System.EventArgs e)
Line1.Height = panel2.Height;
Line2.Height = panel2.Height;
returns the default size of the panel, not the resized panel based on it's content...