Just checked. They're not forbidden, and they're 4 Z-levels underground. =/ Is it a bug? Because don't dwarves also usually move rocks aside if they're blocking where a building is to be built?
Do you have a section of wall that isn't built yet?
Because the only time a dwarf won't move a rock to build a table is when that rock is destined for another job, and mostly that means construction. This would also explain why they aren't being dumped. They're in limbo and nothing will happen until you a) end the construction job using those rocks or b) remove the dump and wait for the construction to get done.
Yeah, there are tons of sections that lie dormant until my wrath cancels and reapplies the task. I wondered that myself. Could the 4 catapults training my engineers and doubling as stone movers be complicating the process too much for the game to keep ahold of?
I doubt it.
But it sounds like you've got an awful lot of jobs that could be using that stone. You have two options.
1) Cancel or suspend every single one of those jobs, un-dump tyhe stone, wait a few minutes to make sure it takes, then re-dump the stone. Re-create all stone-using jobs after your little twits have moved it.
2) Undump the stone, and wait a few game months or game-years. Eventually the dwarves will get around to doing whatever they're supposed to do with it.