Invulnrability Aura Rare Still Provides Protection while Burrowing

I encountered a rare devourer with the Invulnerability Aura affix that was empowering some enemies near it while it was burrowed and without being able to realize it was even there until it emerged from the ground. By then, naturally, I had died from being unable to damage the enemies I was swarmed by.

I sincerely hope this is a bug and not intended behavior.

Bug report id#: 1,208,416,843