I was just surfing around Internet, reading a blog I have just discovered when I have found this post (in french) : http://blogs.msdn.com/nay/archive/2007/10/10/quand-excel-perd-la-boule.aspx
Excel has some calculation problems (or display ?) when dealing with the number 65 535.
Interesting to know no ? ( and to download the associated patch 
)