[XeTeX] optical sizes not found

[Roland Kuhn]

  Hi,

a few days back I asked about a problem with optical font sizes: for me, 
the correct fonts are not automatically selected. I can rule out a 
fontspec bug, since the problem exists also in plain XeTeX:

\font\1="Kepler Std" at 9pt\1
Hallo Welt!
\font\2="Kepler Std" at 12pt\2
Hallo Welt!
\font\3="Kepler Std" at 14pt\3
Hallo Welt!
\font\4="Kepler Std" at 24pt\4
Hallo Welt!
\end

This results in a PDF containing only the KeplerStd-Regular font (no 
Capt, Subh or Disp variants). Now I've had the opportunity to test this 
using the same OTF files on a Windows 7 computer with an up-to-date 
TL2010 installation, and the same happens as on my Mac (Snow Leopard, 
same TL2010 revision).

Could it be that the fonts do not contain some needed hints? (I'm using 
the version from 2003.) How does font selection work on the inside?

Regards,

Roland