"Fast Forward" links don't seem to be correct

If you go to a regular, non-chapter-heading page in the PG docs, such as
http://developer.postgresql.org/pgdocs/postgres/extend-type-system.html
and try the "Fast Backward" link, it goes to that chapter's heading
page, which seems reasonable.  But the "Fast Forward" link points to
the same place.  Shouldn't it lead to the *next* chapter, instead?

This seems to be the case not only in HEAD, but for all the on-line
release versions since 7.4 (the first to have these links).

            regards, tom lane