Think I came across my first Destiny bug today.
It was this Public Event of a Reaver Captain that was doing a route and we were supposed to kill him. He was a level 5 and I was a Level 7 Titan with 2 other people (at least) shooting him and he never lost any health. I hit him with a pulse rifle, then a sniper rifle and finally a rocket launcher and his health bar never dropped.
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Yeah, I ran into him a few times as well. Never was I victorious. Even when using a gun with the same energy as his shield, I couldn't beat him. I figured it was because I was by myself, but maybe it is a bug.