In my case, the modules produced will change xorg.conf and result in the lost of the X environment. I have to remove the modules from the module folder and remove xorg.conf to be able to reboot in X mode.

as per rc1 changelog:Where are the crippled sources?
i have the impression that you are using 'vbox-guest' module on the host machine. please read about the purpose of the guest addon package:In my case, the modules produced will change xorg.conf and result in the lost of the X environment.