XMage, Adding MutateAbility (2)

Got the ETB triggers, by using the 

Ability abilityEquip = new EntersBattlefieldTriggeredAbility(
    new MutateEffect(Outcome.Mutate)
); 

abilityEquip.addTarget(targetNonHuman);

this.addAbility(abilityEquip);

While the MutatesSourceTriggeredAbility failed to trigger..
or probably it is triggered but there is something in the GameImpl
that treated it different way?