[XeTeX] Problem with ITC Stone Sans Std

[Cyril Niklaus]

Hi all,
I'm trying to use ITC Stone Sans Std in one of my documents, but if I  
specify the font like this:
\setsansfont[Scale=MatchLowercase]{ITC Stone Sans Std}, the font  
selected is ITC Stone Sans Std Phonetic, not the Medium. And since  
the Phonetic only has a few glyphs, problems arise.
I know that by specifying Medium, the right font is selected, but I  
was curious to know if anyone here would venture a guess as to why  
the Phonetic fonts gets selected by default.

ITC Stone Sans Std otf, 2003 Adobe.