subselect field "problem"

hi list

i was writing the query below containing a subquery. by mistake, i
referenced a field from the main table in the subquery, leading to a
very strange (but working??) result. the planner announced a insanely
high startup cost, but the query itself finished pretty quickly.

nevertheless, shouldn't pgsql warn the user if he's referencing a
non-existing field in a subquery? the field referenced in the subqueries
WHERE-clause doesn't exist in the subqueries table, thus i don't even
understand why that wouldn't throw an error and how the result would
have to be interpreted:

SELECT * FROM titles
WHERE tit_id IN
(
    SELECT DISTINCT nam_tit_id
    FROM names
    WHERE lower(tit_name) LIKE '%best%'
)

the field "tit_name" is in "titles". the field i intented to use was
"nam_name" from table "names"...

regards,
thomas