Do Wrathgate / Battle For Undercity quest change, one of the best chains in the game and sadly it's going away in cataclysm. Currently in beta the quest chain stops at the cinematic, you never get to go to Undercity.

Source: http://blue.mmo-champion.com/t/26399150318/wrathgate/

Wrathgate/Battle for Undercity gone in Cataclysm
It's not bugged. The quest ends at the cinematic now.