A team from Taiwan server came across the bug.
"When we met the Lich King, a rogue in our team got disconnected at phase 2 and Valkyrie threw our dk down the cliff before we could make any response. Then only eight of us managed to enter the last phase of the battle. Fortunately, the Lich King's first Soul Reap was cast on the disconnected rogue, then we were so surprised to find that the Lich King became a blockhead without any action and just stood there still like a stake."
Dunno whether it works on NA/EU server.