The latest Domain Mapping plugin is a nice addition, but it introduced a bug.
On a site using the original domain (unmapped subdomain) the link to view the site from the dashboard (i.e. top left corner) links to the primary domain with an extra slash at the end (i.e. domain.com//) instead of to the original unmapped domain (subdomain.domain.com).
I've tested this with the new "disable subdomain option" enabled and disabled, after adding and then removing a mapped domain, and on a fresh install with the default settings. All scenarios returned the same bug.