superusers are members of all roles?

I just hit this, which at least violated my sense of least astonishment, 
if it's not an outright bug:

After creating a role foo, I added to following lines to my (9.0) 
pg_hba.conf:

    local    all +foo           reject
    host     all +foo 0.0.0.0/0 reject

The surprising (to me) consequence was that every superuser was locked 
out of the system. I had not granted them (or anyone) the role, but 
nevertheless these lines took effect.

If this is intended, it should at least be documented. But if it is 
intended then it's ugly anyway, IMNSHO, and we should change it.

cheers

andrew