Well, DM plugin had been uninstalled, and there's no way to test it, if can't map the domain to the blog, now is there?
It's not the main blog that is redirecting. It's the domain set to be mapped to a subdomain blog.
For example: I set up a blog site via my multisite, call it test.myblog.com
I try to map blog.name.com to point to test.myblog.com and it redirects to: http://www.blog.name.com with a not found error.
Maybe I did not explain exactly what I meant, before, as it was a long day... LOL