I guess this is a common issue, but I think I've gone through a few similar topics and checked the suggestions I've found there and still can't figure out what's wrong. I figure it has to be something stupid, but here goes:
I built a floor somewhere, then I removed some of the tiles because I wanted holes for a pump stack and walls next to them. Some of the blocks got hauled away, but one stayed stuck on a tile (which was also designated for deconstructing) where I need a wall. It is lying on a floor and below another floor, but is on the same z-level as most of the surface. It does not get hauled, it is not counted when I try to build floors or walls, but is counted in the stocks screen. It also gets ignored when I mark it for dumping as well. I have haulers available, the block is not forbidden, my dwarves are set to gather from outside, and I do have a zone for dumping garbage.
On a possibly related note, a caravan left some junk on the surface that behaves in the same way. The only thing I can add is that the metal items I unforbade and marked for melting *did* get molten, which I find interesting because the other items do not get hauled or dumped.
In both cases, I've tried to claim and forbid a few times to try and jog the game into gear, but nothing's happening. I've also reloaded the game several times since this happened. I don't care much about the caravan items, but the block is in my way. Any ideas what could be wrong?