[XeTeX] Another tipa/xunicode puzzle: interaction with array.sty?

[Alan Munn]

Hi again, I've encountered another puzzle.

% !TEX TS-program = XeLaTeX
\listfiles
\documentclass{article}
\usepackage{xltxtra}
\usepackage{array}
\newfontfamily{\ipafont}{Doulos SIL}
\def\useTIPAfont{\ipafont}
\newenvironment{ipa}{%
\let\stone\TIPAstonebar
\let\tone\TIPAtonebar
\setTIPAcatcodes\activatetipa
\csname useTIPAfont\endcsname
}{}

\newcolumntype{I}{>{\begin{ipa}[}l<{]\end{ipa}}}

\begin{document}
\begin{ipa}[PoP]\end{ipa}

\begin{tabular}{I}
PoP
\end{tabular}

\end{document}

For some reason, the first character of the the IPA environment  
(whether with a newcolumntype or explicitly encoded into the column)  
specification fails to do the correct TIPA mapping.  Enclosing the  
character in braces solves the problem, but this doesn't seem ideal.

Any suggestions?

Thanks

Alan

-- 
Alan Munn
amunn at gmx.com