I think I have a very similar issue with 0.47.04.
A miner got possessed, had claimed a mason workshop, gathered material and started a mysterious construction.
I was busy dealing with a siege and then some internal weremoose problems, so I had forgotten about this moody miner.
Then, I noticed him in a middle of a stairway, not moving. He stays there doing nothing, still "Possessed by unknown forces!". The workshop is still claimed, contains material used for the task.
I tried forbidding the material and reclaiming it. It is not indicated as "TSK" any more. The miner has not reacted.
I used "showmood" in DFHack, this is what is indicated:
[DFHack]# showmood
Bėmbul Uzolginet is currently possessed with intent to claim a Mason's Workshop and become a legendary Miner (but not really).
He has claimed a Mason's Workshop and wants the following items:
Item 1: rock boulder, quantity 3 (got 0)
Item 2: any bones, quantity 1 (got 0)
Item 3: metal bars, quantity 1 (got 0)
Item 4: any logs, quantity 1 (got 0)
(I did not try before messing with the tasked material, because I didn't know about showmood until finding the present thread.)
In the workshop, the bones got back a "TSK" label, but this didn't change what showmood displays. Now the "TSK" label is gone again. The miner still hasn't moved. Now "TSK" is back on the bones. I'm not sure what I do can influence this.
Ah, now the bones are not in the workshop any more, so maybe someone else took them.
I don't find this dwarf in the combat logs.
Curious bug.