I had my iPhone 4 plugged in, but turned off overnight, this morning, I turned it back on, quit all the open Apps and then restarted (holding the home button and power button). Since then I've noticed some of the settings have reset to the default. The Ringtone and Text tone have reset to Marimba and Tri-tone respectively and the 'Show Preview' message setting had reverted to On. Phone is not jail broken, the other settings remain how I had set them. Has anyone else seen this behaviour?