[XeTeX] XeTeX and Arabic

[Musa Furber]

Mr. Kew,

Now that my segmentation fault problem is fixed (many thanks to both 
you and Adam Lindsay, and my apologies to everyone else for the slurry 
of messages), I tried the Arabic.tex example with the (very small) 
catalog of Arabic fonts I have.

The Arabic fonts shipped with OS X worked as expected and desired.

The fonts I have from elsewhere (Windows, for example) behave as 
expected but not as desired: the proper letter is shown, but not the 
proper glyph given the adjacent letter. I wrote "expected," because 
this is what often happen in other applications; changing the font to 
one of the Arabic fonts shipped with OS X fixes the problem.

Is there any way to solve this?

Regards,
Musa