What could throw this into the url?

For some reason, in my url “/page.php?category%5B%5D=1&do=list
its inserted that random %5B%5D, what could cause that? when I trim it down to category=1&do=list I get errors
these are the lines that the error is meant to affect.

[code=php]
function fetch_categories($multiple = true, $unique = null) {
global $vbulletin, $itoptions, $permissions, $vbphrase;

$_REQUEST[‘category’];

if ($options[‘enablecategories’]) {
$catlist = $vbulletin->db->query_read(‘
SELECT * FROM ‘ . TABLE_PREFIX . ‘categories
‘ . ($permissions[‘canviewhiddencategories’] ? ” : ‘WHERE public = 1’) . ‘
ORDER BY displayorder ASC
‘);
$selected[‘category’] = is_array($selected) ? $selected : array();
while ($category = $vbulletin->db->fetch_array($catlist)) {
$categories .= htmlspecialchars_uni($category[‘title’]);
}
$vbulletin->db->free_result($catlist);
}

if (!empty($categories)) {
$categories = ‘<select class=”bginput” name=”category[]” id=”categories’ . ($unique === null ? ” : $unique) . ‘”‘ . ($multiple ? ‘ multiple=”multiple”‘ : ”) . ‘ size=”‘ . ($multiple ? 4 : 1) . ‘” onchange=”manageCatList();”>
}

return $categories;
}[/code]

This is working with vbulletin software (which shouldn’t really be important)
Any Help given would be appreciated.

Also in #PHP _↴