GDI+ Graphics.DrawString repeatability
GDI+ aims to support resolution independence. The exact pixel alignment of text depends on many factors.
Even with the same font, format, text and bounds, the pixel registration of the entire string isn’t constant.
The Graphics object may have state that controls. ClipBounds isn’t it.
http://support.microsoft.com/default.aspx?scid=kb%3ben-us%3b307208