usually the settings are first set upon a new device being connected- when you first plug your USB key/SD Card/Hard Drive into rekordbox the my settings window will pop up- just click "apply on all devices" usually after its done even if you change your settings for some reason it doesn't update the device automatically... so you'll have to reopen my settings again and verify the settings r right then again click "apply on all devices"
I re-started a new hard drive once my nexus players came in and kept the same settings ever since (with SYNC-OFF!) :D