404 errors not displaying

Lately, I’ve noticed my installation of WordPress hasn’t been intercepting 404 errors correctly. Whenever a user visits a non-existant page, it displays a very broken loop of posts AND pages (and even pages that aren’t supposed to be displayed).

See for yourself.
http://www.bradkovach.com/thisisa404error/

I was using the Redirection plugin found at http://urbangiraffe.com/plugins/redirection/ and I removed it and its settings.

I am not modifying the loop queries on ANY page except for the home page and I rewind changes by running <?php query_posts($query_string); ?> after each change.

What could be the problem?

For those that are interested in assisting, I can give over shell access–if you give me your public SSH key. (bradkovach AT gmail DAWT com)

Plugins activated:
Akismet
1blogcacher
WP-UserOnline

This problem occurs with ALL themes.

Here is my .htaccess file

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

ErrorDocument 404 /index.php?error=404

php_value post_max_size 100M
php_value upload_max_filesize 100M

<IfModule mod_expires.c>
ExpiresActive On
        ExpiresDefault                          "access plus 1 week"
        ExpiresByType image/gif                 "access plus 72 hours"
        ExpiresByType image/jpeg                "access plus 72 hours"
        ExpiresByType image/png                 "access plus 72 hours"
        ExpiresByType text/css                  "access plus 1 week"
        ExpiresByType text/javascript           "access plus 1 week"
        ExpiresByType video/x-FLV               "access plus 1 month"
</IfModule>