The log files are automatically rotated each time you restart the server. But after you already have 7 log files for a given day, if you then restart the server, then it will not create a DATE-8.log.gz, it will instead save it as DATE-7.log.gz, and then move DATE-7.log.gz into DATE-6.log.gz, and DATE-6.log.gz into DATE-5.log.gz, and so on, in the end resulting in DATE-1.log.gz being deleted.

Blindly deleting log files is problematic, and if the amount of log files is to be limited, it should at least be made into an option (allowing for unlimited log files as well.)