When I spawned an iron golem while the iron blocks were being moved by pistons, the golem spawns correctly, but the iron blocks persist. On the f3 menu, the game recognizes the iron blocks correctly, but when broken in Survival mode, the blocks drop nothing. When the iron blocks are interacted with, they disappear.

Video: https://www.youtube.com/watch?v=2J6IX767R08&t=1s