Enchantment Devourer dont on hit damage for shaco's dammy(ult)

I mainly play semiTank AS shaco. When I play Devourer shaco,there is no effect with Jungle Item Devourer's on hit damage by Shaco's dammy(ult). But Wits End's on hit damage is effective by shaco's dammy. Is it Bug? (patch5,24)