The bug

When spawning a snow golem in a warm biome, such as plains, they can still create a path of snow at y=67 and above. According to the wiki and MC-377, this shouldn't happen.

Code analysis

The following is based on yarn 1.15.1 names.

In the method net.minecraft.entity.passive.SnowGolemEntity.tickMovement() it has the if-statment for if a snow layer should be set. As MC-377 states, it checks for biomes but since Java Edition 1.7.2 added temperatures, it not longer uses biomes; it uses temperature. When the temperature goes below 0.8, snow will generate. Code wise, this would mean it's intended, but, it might not be (due to MC-377). Suggestion fix (if not intended), would be to check for biomes and temperature.