Very Strange BAD REQUEST Error

I am getting BAD REQUEST errors on my production server

http://newyorkna.org/test/ <- Try the popup menu

This only happens on the production server (I cannot reproduce it on any test server), but it happens with every single browser. It’s a server-level issue. I have traced the AJAX and the redirector (the server fetches from the main server, and then routes the results back).

The main server sends the text back to the router. No problem.

However, inside of WP, instead of sending the text back, as works on every other server, it decides to throw a 400 header.

I see this happening in my plugin, but it also seems to affect other plugins.

The code is here:

http://plugins.svn.ww.wp.xz.cn/bmlt-wordpress-satellite-plugin/tags/2.1.8/bmlt-cms-satellite-plugin.php

Do a search for “ajax_router”, and the execution block is the part within “elseif ( isset ( $this->my_http_vars[‘direct_simple’] ) )”

The code that returns from the main server is exactly the same as that for other servers, except this server throws a nutty over it.

I’m sure it has something to do with the server configuration, but the error appears to be a WP one, so my ISP will bounce it back to me unless I can figger out what switch they need to throw.

Even so, I’ll bet there’s a workaround I can code into my plugin. Maybe I’m not doing something right. I’ve been using this method for years, and it has always worked.

Any ideas?