pg_ident.conf not working?

I've noticed a difference in postgresql 8.3 and 9.0.1 that I suspect
is a bug.  pg_ident.conf isn't working the way it used to.

I have a website set-up with apache running as using user
"www-data".  As I remember it, I found that it was difficult to
set-up a postgres user name with a hyphen in it, so I fell back
on creating a "www" postgres account, and I used the mapping:

pg_ident.conf:

  # MAPNAME       SYSTEM-USERNAME         PG-USERNAME
  apache          www-data                www

That used to work with postgres 8.3 (running on the same
box as apache, of course), now with postgres 9.0.1 I can't
get things like this to work:

pg_hba.conf

  # TYPE  DATABASE    USER        CIDR-ADDRESS          METHOD
  local   my_dbname   www                               ident

The log shows the error message:

  LOG:  provided user name (www) and authenticated user name (www-data) do not match
  FATAL:  Ident authentication failed for user "www"

I can "fix" this by changing "ident" to "trust", but I'd
rather restrict access to just the apache user.

(Hm... maybe I need to try "ident map=apache"?)