Comment 10 for bug 522328

Marco: Why did you install nvidia-173 instead of nvidia-current? Do you have /usr on a seperate partiton? It looks like nouveau isn't getting blacklisted, and if thats the case https://bugs.edge.launchpad.net/ubuntu/+source/nvidia-graphics-drivers/+bug/538071 is your bug.

Federico: That is the intended behavior, you have an xorg.conf speciftying nvidia to be used which is not available for the kernel you are on so it falls back to failsafe. Did you not enable nvidia-current in the restricted drivers manager after you were in failsafe? It should *not* automatically load the proprietary drivers from nvidia.com that you installed in that scenario, those require a manual update every time you update your kernel. I will bring this up with the people making that wiki.