Success! So I've managed to kill the stupid thing
Though without sacrifice....most of my recently saved SAI sketches were damaged. My JPEGs and PNGs were OK, but for some reason, the .sai pics after the date 03/01/13 don't open correctly and I get the message "キャンバスを開くことができません" (canvas unable to open"

Here's what the little bugger looks like:


Remember guys, the internet is a wild thing.
ALWAYS USE PROTECTION

Now I'm off to redo CC15 (￣◇￣ )