1 redirected domain does not go to the correct 404 response

I have a multisite where I'm redirecting a second and third domain to one of my sub-domains (I'll call it domain1.com) using DNS at my registrar. I have a custom message in my 404.php file in the theme directory used by domain1.com. A direct request to domain2.com and a "page not found error" from domain2.com goes to domain1.com with the proper 404 response. A direct request from domain3.com goes to the domain1.com but a "Page not found error" from domain3.com returns the 404.php from the primary domain's root directory which has nothing to do with domain1.com. Although the redirected domains are at different registrars- as best as I can tell they're both configured identical. I tried flushing my local DNS but the problem still persists. Ideas anyone?