Blue Buff Wasn't Attacking Me

I was playing DJ in a Blind 5v5, and I decided to take the enemy's blue buff. It just stood there, sort of slow-walking in place to the side, not attacking. The smaller golem things attacked me, but the big one didn't hit me, even when I moved from behind bush, to in bush, to in front of it. By the time it started attacking, it had maybe 100-200 HP left and didn't matter.