In the process of installation we need to remove packages that are only needed in live mode. Some of those are related to Virtualbox. It seems that we have been a bit too rigorous with that. So if you install 2017.01 in a vbox, you will have a strange resolution as a result.
To fix this for now, just install the packages virtualbox-guest-dkms virtualbox-guest-utils virtualbox-guest-x11 to your installed system in vbox and reboot. We are fixing the problem and will upload a fixed package asap. I will let you know when that is available.
