Index and functions

If I create an index based on a function, as:

create index fubar on table (function(field));

and then I later:

drop function function(...);

It makes it impossible to pg_dump a database until one also explicitly drops
the index. This happens in 7.0 and I haven't checked it 7.1.

If it were my code, I wouldn't call it a bug, I'd call it user error, but there
should, at least, be some mention of this in the FAQ or something.