It is a fundamental flaw in the design of the battle. It is based on a pre-scripted choreographed dance routine, and deviation from this script can result in sudden and illogical corrections.

Basically, Iffy is doing a dance: 1, 2, 3, 1, 2, 4, 1, 2, 5

But if you skip a step and go: 1, 2, 5

Iffy will correct and quickly jump to his new spot (and in this case it means Hellfire).

To be honest, it's so scripted I would expect some botting on him to be happening o.o