CE Version 9 static pages https redirect

Today I have successfully upgraded my gitlab ce from 8.17 to 9 (omnibus package on a Ubuntu 16.04.2 LTS). A few weeks ago I configured to ability to use static pages without ssl in my gitlab.rb config (https://docs.gitlab.com/ce/administration/pages/index.html#wildcard-domains):

pages_external_url 'http://static.....de'

In version 8.17 my static pages were served successfully build and served under the given subdomain on port 80. In version 9 the build process is successful but if I try to access the page in the browser it redirects me from port 80 to 443.

I've added

pages_nginx['redirect_http_to_https'] = false

in my gitlab.rb config to set the default configuration explicit with the same result.

Is this intended to force the usage of ssl, a general problem or only in my installation?

Addtional info: My gitlab instance is available via ssl.