I made an Iron farm with a 5x5 spawning platform above a 5x5 platform on which I placed the villagers. In the center of the villager platform I dug down three blocks and placed a wall with running water so the zombie I placed would bounce (note: I built this in a bay so the zombie is in a glass box under the water.) I placed 4 beds around this hole and placed the villagers on the beds. I surrounded the 5x5 spawning platform with 3 tall glass block walls. I placed a hopper in the center north side of the 5x5 spawning platform going into a chest that is under the glass wall. i used signs and an iron trapdoor to hold the lava source and put water sources in southern corners of the spawning platform. I also placed a glass block on the trap doo to prevent spawning. This concludes the actual iron farm. the bug appeared as i was decorating the build. A golem spawned in the glass wall above the chest. I figured this was a bug and the iron was trying to spawn on the chest and got stuck in the glass, however later another golem spawned in the glass no on top of the chests (as shown in the picture). However this only occurs occasionally and I could not replicate it in a super flat redstone ready creative world. I feel the bug is similar to MC-148955 but that was for previous versions of minecraft.