Major Description
The code in LoggerConfiguratorIni that parses the additivity setting does a check on the value of the config option to see if it is empty() before it applies it - since this option has previously been parsed by parse_ini_file any falsey values will not pass this check, so additivity cannot be disabled.
I've attached a patch which removes the check. Additivity is still on by default should the option not be set, so everything seems to work as normal otherwise.