I just registered a new domain with dreamhost and set it up to work with my existing hosting plan, which has been active for quite a few years now. In addition to this new domain, I have 4 or 5 others, each of which has their own database at something.domain.com.
When I try to create a new database on the new domain, even if I specify a new hostname, it puts the database under the domain of one of my old hostnames.
Example, the new domain is abc.com, and I have an old one called data.xyz.com. When I try to set up a new database with the hostname data.abc.com and a database name of "db" - it sets up the "db" database under data.xyz.com.