Column reference X is ambiguous?

Hi!

SELECT count(rf.userid) as count, rf.userid FROM read_faq rf,
faq f,deltagare_saved d, person p WHERE rf.id = f.id AND f.kursid=20
ANDd.course_id = f.kursid AND d.userid = rf.userid ANDp.userid = d.userid GROUP BY userid
ERROR:  Column reference "userid" is ambiguous


All of the tables have a userid, yes, but this query didn't
fail before 7.1.x. Is it really OK to fail in this case? I
thought SQL standard requires all GROUP|ORDER BY arguments to
acutally exist on the SELECT target list. Then, this makes me
puzzled... Are the joins making the userids get included in the
target in some hidden way?

/Palle