I don't know if this is a bug or a missing feature but in my opinion it is necessary for security reason.
When I publish an internal HTTPS site with WAF it doesn't check if the internal certificate is valid and issued by a trusted CA. My internal web server uses a certificate issued by my internal Microsoft Enterprise CA. This CA is not know to the Astaro box but I can publish the website without any problem.
In my opinion this should work like the Web Security HTTPS Proxy. I should have to import my internal CA certificate so that WAF can build a "chain of trust" (or how want to call it). If the internal certificate can not be validated there should be no access to the internal webserver.
Greetings,
TPok