That is indeed one somewhat interesting screenshot

[AtomicKitKat]

What I want to know is how he was able to leave the Arreat Summit  :blink:

Town Portal. Actually, he might not even need to. Just being able to run one screen out of sight of the boss is usually enough(I've seen less, whereby you trigger a boss unknowingly, then had to walk around a wall, and by the time you arrived, the boss had reverted)

I wonder if this was a "feature" to "punish the cowards" Whatever the case, it's pretty irritating, and I'm sure glad it doesn't affect Act Bosses.