I imagine you were freaking out as much as I was. After a switch from LAMP to nginx/php-fpm/FastCGI and using OPCode PHP caching I've had a few batches of weirdness because of all the caching going on (but a wickedly faster/leaner server).
It didn't spring to mind immediately because I was, as mentioned, freaking out. Glad it was an easy fix that I got to quickly. I think "clear your PHP cache" is probably going to become my "did you try turning it off and then on again?" whenever I have similar problems in the future.
If you're in Vancouver, BC in a few weeks, come on out to our live podcast! https://www.causticgear.com/event/caustic-soda-space-disasters-in-3d/