Mixed Content behind TLS terminating load balancer

I try to setup keycloak behind a load balancer which terminates TLS. I have configured keycloak to not use https with ./kcadm.sh update realms/master -s sslRequired=NONE
And added proxy-address-forwarding="true" on my http-listener as mentioned under “Setting Up a Load Balancer or Proxy”.
Everything seems good so far, except that the keycloak.js is loaded over http which results in error messages due to mixed content, when I want to go to admin login page. I looked into the html code and saw, that other resources are loaded relatively. But the keycloak.js file has an absolute URL with HTTP protocol prefix.

Is this a bug or intended? Or did I make a mistake?

I am using keycloak 9.0.3