Could it be the same problem as here (not in Virtualbox, but with 12.10 installed and an extended partition) :
https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1080701
Could it be the same problem as here (not in Virtualbox, but with 12.10 installed and an extended partition) :
https:/ /bugs.launchpad .net/ubuntu/ +source/ ubiquity/ +bug/1080701