After updating my Arch desktop, the normally symbolic, mono-color icons in the upper-right corner of my Gnome Shell desktop were displaying as full-color icons. I also noticed that during login the first attempt would fail, while the second would succeed. Searching around, I found this Redhat bug where they theorize that the gdk-pixbuf cache was broken as part of the upgrade.
Sure enough, that brought me to a Google+ post in the Arch community that held the solution.
Update the Pixbuf Cache
sudo usr/bin/gdk-pixbuf-query-loaders --update-cache
After that, restart Gnome Shell with
ALT + F2 then
Error in Logs
For anyone searching by the error message.
Failed to load /usr/share/gnome-shell/theme/close-window.svg: Unrecognized image file format