Just took my 50 invuln tank to PI,
Waited for others to attack MOBs, walked into melee, invinc took aggro within 2 seconds.
Same scenarios, attacked and aura after they had MOBs to half health, I attained and kept aggro.
Exemped to a lvl 25 tram, radios in Talos,
Waited for team to engage groups, walked in, taunt, I took all aggro, nothing peeled off.
On an invuln tank, not seeing a bug.