Witch huts generated by new world generator don't spawn witches

The bug

Witch huts generated by new world generator doesn't spawn witches. Only one pregenerated witch is spawned.

How to reproduce

Example I

Seed & coordinates:

-9144014475768710727
/teleport @s -220 69 20

make some floors and big roof in place of witch hut, after that run several times:

/kill @e[type=!player,type=!witch]

Watch what spawns at the witch hut location.

Example II

Seed & coordinates:

ILoveMojang
/teleport @s 825 68 -863 200 0

Preparation for best conditions:

/fill 832 64 -888 838 71 -896 minecraft:air
/fill 822 73 -868 858 73 -916 minecraft:stone_slab
/fill 832 69 -888 838 69 -896 minecraft:acacia_bark
/fill 832 66 -888 838 66 -896 minecraft:acacia_bark
/fill 832 63 -888 838 63 -896 minecraft:acacia_bark

then repeat:

/kill @e[type=!player,type=!witch]