Custom search not working

Hey,
I tried your plugin with the default meta_key which works fine. I’m using Advanced Custom Fields to provide other values like Artist. In those fields I provide band names without “the”. Anyway, chosing the customfield ‘sorting_artist’ I’m getting various plugin errors:

– Undefined variable: ob alphabetic-pagination/inc/functions.php on line 638
– Undefined variable: cb alphabetic-pagination/inc/functions.php on line 639

and the main error appears in header/footer:
[Unknown column ‘wp_postmeta.meta_key’ in ‘where clause’]

It seems that this plugins is hooking into every query, not only the main one. The filtering itself works fine but it seems to be interferring with other queries of the theme/other plugins/custom querys..

One of the error queries (interfering with sort out of stock to the end):
SELECT wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.ID IN (23,5,35) AND wp_posts.post_type = ‘page’ AND (((wp_posts.post_status = ‘publish’))) AND (wp_postmeta.meta_key = ‘artist_sorting’) AND (wp_postmeta.meta_value LIKE ‘f%’) ORDER BY wp_posts.post_title ASC

Is there any way to let the plugin only work for the main query, not some header stuff?