Sort:  

Oh the effect was due to excessive acidity causing the sourdough to die, as it was left being active for too long before baking. A real shame :( Maybe a better post tomorrow.

Ah, overproofing. You can try and save as much of it as possible by putting the loaf in a baking tin, though it will have an odd shape anyway.
Do you bake a lot?

Well not even overproofing, but instead the sourdough only killed itself before the baking even started. Odd things happen.

I don't bake as much as a serious hobbyist or a "real baker", but I've baked far more than average men ever will bake :)