Database visible via mysql CLI but not MOD_PHP with same username

I have encountered a "hidden database" issue with mod_php, apache2 and mySQL that I have thus far been unable to resolve. I am able to connect to the mysql socket using mysql_connect, but then find that mysql_list_dbs only returns the "test" database. This *sounded* like an issue with the SHOW DATABASES privilege until I found I was able to log in to the same MySQL server *as the same user* with the provided command-line client (mysql) and SHOW DATABASES would display all the other databases on this system. Furthermore, I tried connecting as root, and again found only the "test" database was visible to PHP. If I dropped the test database, no databases were visible to PHP (regardless of how many databases were visible using SHOW DATABASES). If I created "test", "tester", "testing", "hello" etc, then the "test" database would reappear to PHP, but no other databases were visible. I also tried to connect PHP to MySQL as a super-user, and encountered the exact same issue. Any advice appreciated, M.