Responding to my own post......the problem was that one of the characters that I used in the password was not being properly quoted before being submitted to the db. Once I changed the password, the user "ubb" was able to pass all the tests.
Here's the final privileges of that user (password munged as before):
mysql> show grants for ubb@localhost;
+------------------------------------------------------------------------------------------------------------+
| Grants for ubb@localhost |
+------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'ubb'@'localhost' IDENTIFIED BY PASSWORD '*123456789' |
| GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER ON `ubbthreads`.* TO 'ubb'@'localhost' |
+------------------------------------------------------------------------------------------------------------+
