I tried this out as well to see what people are talking about on my Rad/Fire Brute. Bosses and Lts would run away the longer the fight went, but would immediately re-engage if I hit them with any attack. Funny thing, I tried it without Burn, Blazing Aura or Irraditated ground running (in various combinations of one off to all three) and still saw this happen. I never noticed this activity on Test while trying out a Tanker equivalent of the same setup, so maybe this is something that is being caused by the Gauntlet/Punchvoke procs reaching mob saturation.