domain mapping a multi-domain site cause all sites to redirect to the domain mapped

I have setup a domain as multi-domain:

(1) subdomain.otherdomain.com

and created a site under it

(2) subdomain.otherdomain.com/home

now I want to make (2) as (1), it work. But I also want to create another site

(3) subdomain.otherdomain.com/myname

but when I want to access (3), it redirect to (1). Is it a bug or it could not handle my requirements?

My objective is to be able to use 1 wordpress installation but can use multidomain & domain mapping to look like I have multiple wordpress installation.