MT 3.2 on a FreeBSD server running perl 5.8.7.

I have a link in each of my monthly archives to go to the previous one. Here's what it looks like:

CODE
<MTArchivePrevious>
<p class="right">
<a href="<$MTArchiveLink$>" title="Go back one month">Keep going back »</a>
</p>
</MTArchivePrevious>


It works fine, except when the current month is January. When the month is January, it skips back a full year!

http://www.chellman.org/mt/archives/2006_01.html

Actually, I take that back, that only happens until January 2004.

http://www.chellman.org/mt/archives/2004_01.html

From that page, I can go back to December 2003.

I have entries for every month of the problem years (in fact, every month back to 2000). I haven't found any known issues anywhere. Is there something I should check?