This is....odd to say the least. At least with the plasma pistol, I've just noticed, too late mind you, that using the gun to hit an enemy (muton navigator in this case, non-MC'ed at the time, other than panic attacks, and on that score, muton navigator (last alien. at least I think so, laser tank on patrol hasn't revealed much other than landscape, snipers taking overwatch w/ their flight suits and heavy lasers haven't seen anything, the odd alien grenade in buildings and IC rounds fired into farmer's fields haven't sent anything green and ugly scurrying out, UFO thoroughly explored, alien detained for practice on command bridge)
Thing is basically being kept alive for psionic training and so a rookie can eventually get there and execute the thing.
But I noticed, too late, that giving it a beating with a soldier's plasma pistol was decrementing the ammo counter, and when it reached zero, figured what the hell, shouldn't stop it being used as a club, but it did, the soldier could initiate the attack itself but it crashed the game.