pre_comment_approved hook manual telling wrong things.

Hi, maybe here is wrong place to write this post,
but i found one wrong thing in codex manual.

It’s about pre_comment_approved filter which returns
comment status. This page is writing that i can return 0 or false
and 1 or true. but when i’m trying to return true or false value my comment disappears
from my admin panel. Then i found my comments
in “comments” table which “comment_approved” field is blank in the datebase.
It works fine when i’m return 0 or 1 ,and dont work when i return true or false.
If i’m wrong please tell me the reason.
Thanks.