Seeing weird behavior with my URL being changed from a CNAME to an A record

I’m trying to test some odd CORS behavior in an API of mine. When I send the OPTIONS request in Postman to my friendly API name, I get back a 400 Bad Request. But when I actually hit the API from a website, it works. So i dug into the load balancer logs, and I found that the OPTIONS requests that worked were sent to the URL just as I had typed it in, but the ones that failed from Postman had the URL rewritten to the ugly URL that the friendly URL points to with a CNAME record. Is this a known behavior in Postman? If so, is there a setting somewhere to disable it?