Today, I decided to restore my ultrasn0w-unlocked iPhone 3GS from 4.1 to 4.2 GM. I accidentally clicked option-update instead of option-restore in iTunes but by the time I realized this, it was already too late and I couldn't stop the update process. I thought the phone would brick or something, but when the phone started up again, I found that the firmware was no longer jailbroken, but the unlock was preserved. Can someone explain this surprise to me?