Comment 3 for bug 701395

I was getting the same error about garbage metamode, and believe it may have been related to the following metamode in my xorg.conf:

Option "metamodes" "nvidia-auto-select +0+0"

This was set by default when I installed the nvidia proprietary drivers. I went into the nvidia-settings and enabled my laptop display, setting the resolution to its native one rather than "auto". Now my xorg.conf has the following:

Option "metamodes" "DFP-0: 1920x1080 +0+0"

I've yet to see the garbage metamode again. Perhaps it is coincidence, but I'll continue to watch it.