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.
Attachments
Comments 16
Shows that biome is in Plains. Snow Golems will only make paths in Snow related biomes, thus dupe of MC-377
Hmm... probably something changed in the Mob AI that affected the Snow Golem with making snow sheets.
Please remake the screenshot with F3 enabled.