I have a network install that was running fine with all 5 mapped domains working as expected. The client asked that the primary domain for 2 of the sites be changed.
These URLs already existed as secondary URLs in the Domain Mapping plugin. I am not sure what the DNS record was for them prior to the change request.
The 2 URLs now have A records pointing to the server IP, but each is generating a time out error. If the URL entries are set to "Primary" in the DM plugin, the 2 blogs are unreachable. If they are not set as "Primary" the blogs can be reached via their network subdomains.
I downloaded and installed the development version of the plugin yesterday. Changes made in the plugin admin panel are changing in the DB.