I've messed up the admin search functionality. Help!

This all started because, on the front-end, I wanted the search query to include terms from taxonomies and custom meta. So, after a google, I found the following code which I added to my functions file:

add_filter('posts_where', 'advanced_search_query' );
    function advanced_search_query( $where )
    {
    if( is_search() ) {

global $wpdb;
$query = get_search_query();
$query = like_escape( $query );

// include postmeta in search
 $where .=" OR {$wpdb->posts}.ID IN (SELECT {$wpdb->postmeta}.post_id FROM {$wpdb->posts}, {$wpdb->postmeta} WHERE {$wpdb->postmeta}.meta_key = 'bible_reference' AND {$wpdb->postmeta}.meta_value LIKE '%$query%' AND {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id)";

 // include taxonomy in search
$where .=" OR {$wpdb->posts}.ID IN (SELECT {$wpdb->posts}.ID FROM {$wpdb->posts},{$wpdb->term_relationships},{$wpdb->terms} WHERE {$wpdb->posts}.ID = {$wpdb->term_relationships}.object_id AND {$wpdb->term_relationships}.term_taxonomy_id = {$wpdb->terms}.term_id AND {$wpdb->terms}.name LIKE '%$query%')";

if(WP_DEBUG)var_dump($where);
}
return $where;
    }

It worked a treat for my front-end search. However, I’ve since discovered that the admin search has now gone to pot. For example, if I search in the list of pages in the dashboard, it only displays results from my custom post types. And, if I try searching again, once the first lot of results is displayed, I receive an error: ‘Invalid post type’.

I’ve tried removing the filter using remove_filter() but nothing seems to work.

Please can someone help?