polygonal walls and adjoining walls go mad in 3d

[Anonymous]

anyone know where the wierd shape that is part of the highlighted wall (an ordinary straight wall) has come from? everything looks fine on plan, but not in section and 3d views.

it seems to be to do with the join between the highlighted wall and the neighbouring polygonal wall (to the left). When i move the two walls around the model together there are places where it works fine (clean join, no odd shapes) and places where all these random shapes intersect with the walls. But i have all the layers turned on, and there's nothing there! so where are the wierd shapes coming from? When I move the whole model, the odd shapes change, as if there's some sort of SEO going on with objects i can't see that have remained stationary whilst the whole of my model has moved. This happens with all the polygon wall to normal wall joins in the model. Everything else looks fine.

If this is blindingly obvious or covered somewhere else i'm really sorry (i did search for it), but i'm totally stumped. Any ideas?