HTTP Subdomain Redirect to HTTPS automatically. Why?

I have two websites deployed in IIS 7.5 Express. The first website is the PRODUCTION website and the second is the TEST website. In the PRODUCTION website, I added an HTTPS binding and Require SSL so it is normal that it will force to redirect from HTTP to HTTPS. In the TEST website, I didn't add HTTPS binding and the Require SSL is disabled, but I wonder why it still forces to redirect from HTTP to HTTPS. Any idea why this happens?

By the way, the PRODUCTION site uses the main domain (www.maindomain.com) and the TEST site uses only sub-domain (test.maindomain.com).

I don't want the sub-domain to only use HTTP, not HTTPS.


I think it's either of these two:

  1. You have used a permanent redirect. The browser caches these redirects and does not ask the server again
  2. IIS uses HSTS. The browser remebers that you page should only use HTTPS and switches always.

For both cases, clearing the browser cache should fix the problem.