Last night saw Left 4 Dead for the Xbox 360 getting a few tweaks in an update. Most important is the ability to recover any achievement progress that was lost when The Sacrifice DLC was released. Not all progress can be recovered, but it should help rectify some of the problems the DLC caused. There are also several other small alterations to the game listed below:
• In Versus mode Tanks will spawn in stasis until a human player takes over. Tanks in stasis are invisible and invulnerable, and won’t move or attack.
• Tank speed is no longer reduced when on fire.
• Allow players on the Infected team to manually spawn during finales.
• Added a vote option to toggle All-Talk.
• Special Infected that causes a Survivor to stumble into a “ledge hang” situation will receive 50 points.
• Bullets that first pass through an infected character before striking a Survivor are now ignored as friendly fire.
• In Versus mode car alarms will now trigger anytime a Special Infected pulls or stumbles a Survivor into an alarm car.
• Survivor Bots no longer try to melee exploding barrels out of their way.
• Fixed the Sacrifizzle achievement.
[Source]