Rapture and aggro

Hey,

I realized that "energizing" my tank when a shield brakes will sometimes have me get aggro. It's not a problem during a fight but mostly in the beginning.

If I pre-combat shield a tank and he takes high damage before doing damage hisself, the shield will break, grant him rage/runic power/mana and I will be attacked. I thought rapture shouldnt give me any aggro.
I never expirienced this before but I havent played on retail, so I dont know if this is working as intended or if it's a bug.
Does someone know?