Valve undecided about Left 4 Dead DLC working in L4D2

Joystiq writes.... Valve raised quite a stink after announcing a new downloadable campaign for the original Left 4 Dead with only a few months remaining until the release of Left 4 Dead 2. What everyone still wants to know is whether this content will be compatible with the sequel -- and we do mean everyone. In an interview with Edge Online, Valve's Chet Faliszek explained that even the game's creators are unsure whether the new campaign will be playable in the second edition of the zombocalypse sim.