Cannot build an iron/snow golem unless a 3 wide 3 long 1 deep hole is dug beneath the materials

When building an iron golem or snow golem on solid ground, the blocks don't update into entity form. I have ensured that I am using full iron blocks or snow blocks respectively, and that a jack-o-lantern is used for the head. I have also placed the blocks in the order they need to be placed for it to work. It does nothing - that is until I dig a hole underneath it. I have found that doing so and then trying again works. So, while i may have found a work-around, I do wonder if there is a possible fix for this in the future.