[XeTeX] segmentation faults in output routine

[Dohyun Kim]

On my macbook (snow leopard) I am currently using XeTeX binary shipped
with tex live 2009 (not MacTeX).

TeX input as follows always crashes xetex in its output routine.

\XeTeXinterchartokenstate=1
\XeTeXinterchartoks 0   0 {\global\futurelet\lastchar\relax}
\XeTeXinterchartoks 255 0 {\startcharstring}
\XeTeXinterchartoks 0 255 {\stopcharstring}
\def\startcharstring{\XeTeXinterchartoks 255 0 {}}
\def\stopcharstring {\XeTeXinterchartoks 255 0 {\startcharstring}}
\pageno=10
Test.
\bye

No error message is shown; xetex just crashes:

This is XeTeX, Version 3.1415926-2.2-0.9995.2 (TeX Live 2009)
entering extended mode
(./test.texSegmentation fault

Surely, no problem occurs if I define the macro \startcharstring as
"\XeTeXinterchartoks 255 0 {\relax}".
But I sometimes have to use empty token list (really empty list even
without \empty macro) for character mapping.

What I have done wrong? Or is this a bug of xetex engine?

-- 
Dohyun Kim