Vacuum-ed Ravenous Myrtle's trait doesn't work

Hello,

Fighting Myrtle I had my Yeti cast vacuum and steal Myrtle’s Ravenous but when my creatures killed an enemy it did not trigger.

Traits you steal from story bosses won’t work for your creatures - otherwise bosses would be far too easy.

Ah fair enough, the spell should fail then or there should be some warning.