[texhax] \addcontentsline -- line added to TOC appears in wrong place. Why?

[Niall Mansfield]

- Using book.cls.
- Redefined \appendix, to add an "Appendixes" heading line to
   the TOC, as follows:

\renewcommand\appendix{
   \addcontentsline{toc}{chapter}{Appendixes}	%% this is the new line
   \par
   \setcounter{chapter}{0}%
   \setcounter{section}{0}%
   \gdef\@chapapp{\appendixname}%
   \gdef\thechapter{\@Alph\c at chapter}}

When we run this on a .tex file of the form:

	\chapter{Last chap}
	...
	\appendix
	\chapter*{APX-1}
	...
	\chapter*{APX-2}
	...

we get the "Appendixes" line in the wrong place.
The .toc file shows this:

\contentsline {chapter}{\numberline {A}APX-1}{53}
\contentsline {chapter}{Appendixes}{53}
\contentsline {chapter}{\numberline {B}APX-2}{57}

What's happening?