I have killed the king many a time. At least in the 15-20 times range.
NEVER seen this.
BTW, past about level 32-33 or so, the king no longer drops cool stuff for you. God bless trivial loot code. Why they put it in this zone made no sense, even before trivial this zone was seriously undercrowded, and the idea of trivial is to aid newbies. Do you realize how few newbies can go to the Warrens? It's just damn inconvienant at times, specially if your a good race/class.
Another problem is if your low enough level to get loot from the king, your low enough to guarntee the high shaman will aid. So soloing you will almost always be facing both.

