Harbinger of Brutality [Or all Harbinger buff bug]

This buff covered by flask effect , phasing ...etc
I dont know other harbinger skills are same as this or not.

edit: even with blood rage kill mobs reflesh blood rage, the buff gone , lol .
edit2 : recast golem , ancestral warchief , same .

It's a bug right ?

The harbinger buffs are periodic. They last for a fixed duration and have a longer cooldown after that duration is up. You do not get to leave them up forever.