It's happened since the early days of Draksis farming, and it's awesome when it happens! I think that, allegedly, there's a chance (frigging tiny tiny chance) of exotics dropping from eligible bosses [i]without[/i] 3 of coins equipped, so sometimes the boss will spooge 2 yellows at once if both occur at the same time. Either that or there is a coin-stack mechanic that sometimes overloads and gushes 2 at you.