Issue with Domain Mapping not pointing to the right place

So I'm using this plugin for domain mapping. The problem that I'm having is that the main domain (staugministries.org) is being replaced in the user's browser with their old domain (staugustinemanor.org). I've double-checked the settings but have been unable to get this to behave correctly, and I'm not sure what to do at this point. I'd be happy to share any information needed to get a little help. Thanks!