Iron golems and withers can't be summoned via building them if there are blocks located near their bases or heads

The Bug:

Iron golems and withers can't be summoned via building them if there are blocks located near their bases or heads.

Steps to Reproduce:

1. Build the setup as shown in the provided attachment. setup.png
2. Place a carved pumpkin in the middle and on the top of the iron blocks in an attempt to summon an iron golem.

Observed Behavior:

Iron golems and withers aren't summoned.

Expected Behavior:

Iron golems and withers would be summoned.

Code Analysis:

Code analysis by [Mod] ampolive can be found in this comment.