Database OID xxxxx now seems to belong to "foo"

Hi:

Trying (and failing) to attach to my DBs. Getting...

database "foo_standby" has disappeared form pg_database

DETAIL: Database OID 2323523 now seems to belong to "foo"

I have 2 dbs... foo and foo_standby. Every midnight, I truncate
foo_standby and load it up with all the current data from mu various
sources. If that's successful, I then rename foo to foo_tmp, then
rename foo_standby to foo, then rename foo_tmp to foo_standby. This
results in a minimal "down time" of the foo database ebcause the renames
happen fast. And foo_standby is now my backup from the previous day,
something I can switch back to if something goes wrong with the new foo
db.

Anyway, "psql -l" does show my dbs. There are other dbs for other
projects and I can connect to those OK. I just can't connect to foo or
foo_standby.

Q: What might have caused this problem and how can I avoid/prevent it in
the future

Q: Can I salvage my foo and foo_standby DBs?

Thanks

-dave