There seems to be an internal difference, too, at least for whether it's DATA_DICTIONARY or data_dictionary:
drizzle> show schemas; ERROR 1044 (42000): Access denied for user 'daniel' to schema 'data_dictionary'
drizzle> use DATA_DICTIONARY; Schema changed
drizzle> show tables; ERROR 1044 (42000): Access denied for user 'daniel' to schema 'data_dictionary'
There seems to be an internal difference, too, at least for whether it's DATA_DICTIONARY or data_dictionary:
drizzle> show schemas;
ERROR 1044 (42000): Access denied for user 'daniel' to schema 'data_dictionary'
drizzle> use DATA_DICTIONARY;
Schema changed
drizzle> show tables;
ERROR 1044 (42000): Access denied for user 'daniel' to schema 'data_dictionary'