Problems accessing databases on remote postgresql sever

I have a postgresql (9.1.4) server running on a remote machine (Ubuntu 12.04), and I'm having trouble accessing it on my local machine. Specifically, on my local machine, I can access the remote server using only the username "postgres" and the database name "postgres", even though I have other user names and databases. First some of the background information. While in the interactive environment invoked with "psql" on the remote machine, I created another user, called "mxtxdb", and set the password for that user. I also created a database called "mxtxdb". To demonstrate their existence, I logged onto the remote machine and ran:

sudo su postgres
Password:
postgres@myhost:~$ psql                                  
psql (9.1.4)
Type "help" for help.

postgres=# \du
                             List of roles
 Role name |                   Attributes                   | Member of 
-----------+------------------------------------------------+-----------
 mxtxdb    |                                                | {}
 postgres  | Superuser, Create role, Create DB, Replication | {}

postgres=# \l
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------
 mxtxdb    | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =Tc/postgres         +
           |          |          |             |             | postgres=CTc/postgres+
           |          |          |             |             | mxtxdb=CTc/postgres
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
(4 rows)

Furthermore, while still on the remote machine, I can access the database from the "mxtxdb" postgresql account:

postgres@myhost:~$ psql -h localhost -U mxtxdb -d mxtxdb
Password for user mxtxdb: 
psql (9.1.4)
Type "help" for help.

mxtxdb=>

But when I try to do the same on the local machine, I get this:

psql -h <server's address> -U postgres -d "postgres" -p 5432
Password for user postgres: 
psql (9.1.4)
Type "help" for help.

postgres=# 

and

psql -h <server's address> -U "postgres" -d "mxtxdb" -p 5432
Password for user postgres: 
psql: FATAL:  database "mxtxdb" does not exist

and

psql -h <server's address> -U "mxtxdb" -d "mxtxdb" -p 5432
Password for user mxtxdb: 
psql: FATAL:  role "mxtxdb" does not exist

The last two lines of my pg_hba.conf file are:

host    all             mxtxdb          0.0.0.0/0               trust
host    all             postgres        0.0.0.0/0               trust

and the listen_addresses is set to '*' (and uncommented) in the postgresql.conf file.

Any idea why I cannot access other accounts or databases remotely, but I can when ssh'd into the remote machine?