hook_db_rewrite_sql is dropping my "select"?

Hi all,

I've only just noticed this problem, because I've been developing logged in as the superuser, but as soon as I try to view a member profile page as an authenticated or anonymous user - basically, as soon as !node_access_view_all_nodes() - I get this warning:

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INNER JOIN node_access na ON na.nid = node.nid WHERE (na.grant_view >= 1 AND ((n' at line 1 query: INNER JOIN node_access na ON na.nid = node.nid WHERE (na.grant_view >= 1 AND ((na.gid = 0 AND na.realm = 'all'))) LIMIT 0, 10 in D:\muun_nobackup\classiccars\includes\database.mysqli.inc on line 151.

As you can see, somehow the "SELECT ..." is being dropped from the query. Very strange! I printed the queries as they enter the node_db_rewrite_sql() hook, and they seem fine:

SELECT nt.type, nt.* FROM {node_type} nt ORDER BY nt.type ASC

SELECT n.nid, r.nid AS node_id, c.*, n.title FROM {category} c INNER JOIN {category_node} r ON c.cid = r.cid INNER JOIN {category} cn ON c.cnid = cn.cid INNER JOIN {node} n ON c.cid = n.nid INNER JOIN {node} cnn ON cn.cid = cnn.nid WHERE n.status = 1 AND r.nid = %d ORDER BY cn.weight, cnn.title, c.weight, n.title 

But when they come out the other side they're all messed up. This is frying my brain. I have no idea where to START working out how/why/where Drupal is dropping the fed in query. Any suggestions?! :-(

Thanks,

G