You are correct. As of 3.4.7, several new 'start-up' styles are provided and the theme automatically loads in the new 'ata_round.txt' style - which is different from the default styling. This was done to give people an new starting look.
The reset button will take you back to the default settings. You should always have a backup of your settings before making any changes. You can do this by doing an EXPORT (if you do this make sure you are at least on 3.5.1) so that if you do mess up, you can reimport your settings.
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Juggledad | Forum Moderator/Support