Strays don't spawn in powder snow

Strays dont spawn in powder snow even though they are immune to it. 

Steps to reproduce:
Create a new superflat world with this preset: "minecraft:bedrock,1*minecraft:grass_block,minecraft:powder_snow;minecraft:snowy_tundra"
Use the command /time set midnight

Press f3 and see how the monster mobcap number wont go up.

 
Polar bears do spawn