Subdomain not redirecting to mapped domain

I just set up a network with domain mapping. The mapped domains are working properly. However, the subdomains are not redirecting to the mapped domain.

For example:

mappeddomain1.com is mapped to subsite1.network.com. When I visit mappeddomain1.com everything works as it should. When I visit subsite1.network.com it doesn't redirect to mappeddomain1.com like it is supposed to. It still shows subsite1.network.com.