This has been a LONG running issue for me, and I never thought to submit it. Due to a recent event, I figured I'd finally go ahead and send it in:
I had a hammerlord get injured fighting undead camels. He was put on bedrest for like, three years with broken legs. I forgot about him, until all of a sudden he had healed and was walking around the mess hall. He did everything that a normal Dwarf should, eat, spar, drink, sleep, buy stuff. But if I activated him he would stand perfectly still and never move. He also had no interest in fighting, never moving towards enemies that might come within range.
Any Dwarf that was put in a squad with him - either under him, or as his leader - would do the "Stand still" trick too. As soon as they were removed, they'd begin to act normally again. Over time, he developed a relationship with another military Dwarf and I put them in a squad together and forgot about them. Something has rubbed off on that second dwarf, because now he has stopped moving too. They aren't in the same squad, and as soon as he's activated he refuses to budge from his spot until that setting is turned off.
I've got a save available if you want it. This happens any time you activate those Dwarves, so it's not something you have to wait a specific time for.
EDIT: I've run a couple tests, and there are some interesting things. If I take the Dwarves and tell them to have no weapon, and no armor, then activate them, they strip all their stuff where they're standing and don't move. If I then tell them to get different weapons and a different class of armor, and they're still activated, they'll run off and collect everything - when they get their last piece of equipment they stand perfectly still and never move to their squad designation point.