Hi,

i ran into sorting issues, so i did some digging.

I do not use comment module, so in this query 'score' returns NULL :
File faceted_search.inc, line 1238$score_field[] = '%d * POW(2, (GREATEST(MAX(n.created), MAX(n.changed), MAX(c.last_comment_timestamp)) - %d) * 6.43e-8)';
Without comment module c.last_comment_timestamp is NULL, and unfortunatelly the function GREATEST() returns NULL too.
Maybe you should consider using IFNULL() like
$score_field[] = '%d * POW(2, (GREATEST(MAX(n.created), MAX(n.changed), MAX(IFNULL(c.last_comment_timestamp,0))) - %d) * 6.43e-8)';

Thanks,
David

PS:
For the reaI best sorting (to order only by created time) I had to remove changed and last comment time from this line.