let us for example take this raw file (Pentax K20D .DNG raw file) - http://www.imaging-resource.com/PRODS/K ... MM.DNG.HTM
focal length is 43mm (reported by PhotoMe, which is correct), however look what we have in XnView if we will try to use <Focal Length> tag
http://img199.imageshack.us/img199/8219/xnviewbug.jpg
I have the same thing with my Pentax .PEF raw files - I used .DNG file just to illustrate the problem w/ publicly available image