When I uncheck the "Web virtual server en-abled" Option of a Virtual Server, I automatically kill the Web Server of all associated Alias Servers.
This is expressed in the warning "Apache website - All Apache directives in the virtual host will be removed." though something like "incl. all Alias (sub-) Servers)" would seem appropriate.
Nothing serious until here.
Next I re-en-able web for the Virtual Server.
When I go now to any of his Alias-Servers and open "Enabled Features", the Option "Web virtual server enabled?" is checked (it had disappeared, while the Virtual-Server had no web feature enabled).
BUT: the Alias-Server is in fact unavailable (=not listed in the .conf and not reachable: I get the Apache default page via http). In order to get it back working, I have to disable the feature, save, then re-enable and save it again.