RandomSpawning ADD Does not work

Enable /gamerule doMobSpawning false and have random spawning files have the ACTION: ADD

and you will see there are no mobs to be spawned.

MythicMobs version: 2.5.0
Spigot version: 1.8.8, 1.9.4

/mm mob killall kills 0 mobs as soon as that gamerule is enabled.