I have installed Pro Sites and also installed Domain Mapping plug-in. Activated both on the network activation from the network sites area. I have two domains pointing to single IP Address for the server. Domain A http://www.domaina.com is the primary that I installed WordPress 3.4.2 (Fresh install) and then I add the two plug-ins above. I add new site via Pro Sites. I followed the domain name mapping instructions with sunrise file moved, updating wp-config, etc. No matter it just always redirects http://www.domainb.com to http://www.domaina.com word press.