While a few days ago at work, I was dropping a hammer on a particular spot to fix a problem, today was spent jackhammering concrete that someone else had poured over some badly-placed rebar so that I could rearrange the supports. I've rearranged a *lot* of supports now and the structure *looks* ok, but on close inspection I can see that something is still wrong.
On the other hand, I have narrowed down the source of the error substantially and the code is being much better behaved. (Bad code! No biscuit!)