meta_query in pre_get_posts

Hi all,
and thanks for reading.

I’m using a pre_get_posts filter to customize a search.
The hilighted part is the tough one.
It seems to cause $query to return a SQL request containing the bad “WHERE … AND 0=1 …” string.

I can’t figure out why is this.

http://pastebin.com/qktr1pP0

Here’s the request string

SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id)
WHERE 1=1
AND 0=1
AND wp_posts.post_type = 'lot'
AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private')
AND (wp_postmeta.meta_key = 'lot_prix'
	AND (mt1.meta_key = 'lot_zip' AND CAST(mt1.meta_value AS SIGNED) BETWEEN '31000' AND '31999')
)
GROUP BY wp_posts.ID
ORDER BY wp_postmeta.meta_value+0 DESC
LIMIT 0, 10