Conflict between xeCJK and hyperref in TeXLive 2012

Question

I find that in the presence together of packages hyperref and xeCJK, in either order, raises an Improper alphabetic constant error with an em-dash in commands \section, \subsection, etc. This happens with TeXLive 2012 but not 2011. Here is an MWE:

%!TEX TS-program = xelatex
%!TEX encoding = UTF-8 Unicode

\documentclass{article}    
\usepackage{xeCJK}
\usepackage{hyperref}            % adds clickable links to TOC

\begin{document}
\section{O my swineherd!}
\subsection{Em-dash --- in subsection}
\end{document}

An en-dash does not cause the same problem.

The temporary expedient of

\usepackage[unicode,psdextra]{hyperref}

offered at http://tex.stackexchange.com/a/69354/3935 does not work here; the temporary expedient of

\subsection{Em-dash \texorpdfstring{---}{} in subsection}

following http://tex.stackexchange.com/a/69338/3935 does work, but I'd rather clear up the underlying problem. Any thoughts?

For now, I've reverted to TeXLive 2011.

Answer 1

I get no error.

Update your TeX Live 2012 online (using tlmgr) instead of reinstall it (older version) time and time again.

Use \listfiles in the preamble to show the versions of your packages in the log. Here is mine:

xeCJK.sty    2012/10/27 v3.0.10
expl3.sty    2012/09/29 v4249
fontspec.sty    2012/05/06 v2.2b
hyperref.sty    2012/10/31 v6.83l