Oh, then it's a bug, a minute ago I uploaded the most current version (fixing some other stuff), but until I'm back at work I won't be able to fix this ...
If you want to provide a patch, I'd be glad to push it
Note: I haven't used the db creation many times in imscp because the option was mostly to migrate existant databases but it should be definitively fixed ..
I don't have a patch but I solved issuing a simple CREATE DATABASE mysql command after calling the imscp_domain --action 'create_db' command.