In the framed theme, there are two links on the left-hand nav bar which are labeled as "Create Sub-Domain".
The first of which is under the "Sub-Server Creation" link, the second is under the "Create Server" link.
The second one works fine. It's the first one where there's a problem.
If you log in as root, and choose the first "Create Sub-Domain" option, you'll instead be taken to the screen for creating a new Server.
If you log in as a user, and choose the first "Create Sub-Domain" option, you'll be taken to the screen for creating a new Sub-Server.
The only way to actually create a sub-domain is by using the link located under "Create Server" at the bottom.
I'm using the new framed theme, from version wbt-virtual-server-theme-2.4-1, but this also occurred in the previous version.