I'm setting up a clean installation of Roundcube 1.6.0 Complete, and the installer totally ignores SMTP fields, user defaults fields, and general config fields... maybe others as well. Seems only the Plugins options were committed, nothing else. Rerunning the config creator doesn't do anything. I've verified read/write access, and no errors are produced saying that config isn't writable. The installer also strips items that I place in the config file manually.
Using PHP 7.4 / IIS 10