The bug

Foxes do not get stuck on powder snow like on snow layers.

Steps to reproduce

1. Make two platforms separated by a 2 block gap, One of powder snow and another of Grass and Snow Layers
2. Place foxes on the powder snow platform and chickens/rabbits on the other one
3. Kill the rabbit/chicken when a fox jumps, before it lands. The fox gets stuck in the snow
4. Now place the foxes on the Snow Layer platform and the rabbit/chicken in the powder snow platform
5. Notice how the foxes just stand on the powder snow instead of getting stuck

Code analysis

Code analysis can be found in this comment.