Calendar in include doesn’t update

I’ve got a 1.2 blog for which I put the menu in a php include — including the calendar:

<?php include("https://designerjones.com/incl/sidebar.php"); ?>

Top of include file:
<?php
require('../wp/wp-blog-header.php');
require('../wp/wp-config.php');
?>
which includes:
<?php get_calendar(); ?>

The include works, including the calendar *links*, but the calendar itself doesn’t update when you move from month to month. Click on the previous month link (which does take you to the correct page) and the calendar info does not change — it shows the current date. Open a different browser, clear the cache, dump cookies and go directly to the first post (made in April), and the calendar displays the current date (that is, it’s June 2005).

My permalink structure is: /%year%/%monthnum%/%day%/%postname%/

The above works on every WP 1.2 installation where the calendar is in the template rather than an include. This makes me think that the include file may be being cached or perhaps get_calendar won’t work in an include. I’ve searched the forums and Codex but haven’t found a solution. Would anyone have any hints about how to solve this, or where to turn?

The site: https://designerjones.com