As above.
On the Guldorand server, initiating combat from invisibility or stealth causes a copy of the mobs to appear in (at least) the Eagle. Double-checked communications with the Eagle-side victims: the boss spawns at the point with the copies, but despawns from the side of the person initiating combat.
On the Distant Shores server, initiating combat from invisibility or stealth causes a copy of the mobs to appear in the pet shop. I don't remember the name.
It does this regardless of the exact method that combat was initiated by so long as stealth/invisibility is used. It was tested with melee attacks, ranged attacks, and spells. They did not report any copies spawning when we attacked without stealth/invisibility.