I am trying to confirm this with both of my thralls having a shield equipped. I ran the thralls through a shattered spring exp run this morning a few times and not once did the thralls get stuck in the shield block position. Once the server comes back up i will continue.
I did not see anything about it being fixed but i could have missed it. Unfortunately thralls are still falling through the ground occasionally when fighting large mobs but its a start if it holds true.