Hearthpwn

I was playing Keleseth Rogue earlier today against Big Priest. I had a Drakonid Operative in play, and my opponent summoned a 5/5 Obsidian Statue. I played Deathspeaker and promptly bounced him back to my hand, assuming that the "immune" status he provided would protect my Drakonid Operative, but he died to the deathrattle all the same.

Is this intended/known? Does it really just mean you're immune to targeting and damage? I'm a bit surprised, since that Ragnaros tavern brawl featured an immune minion that seemed to be truly unkillable. 

Immune minions have always been able to be killed by untargeted destroy effects. 

See https://hearthstone.gamepedia.com/Immune for a full description of how it actually works.

Thanks!