This is a patch that's a long time coming, as it applies to the original Left 4 Dead on the Xbox 360. For those that purchased the Sacrifice DLC for the game, they may have found that it not only erased the progress of some other achievements - namely the Zombie Genocidist - but that certain achievements were unobtainable like one called Sacrifizzle. Thankfully, Valve have stood by their product and released a patch that fixes these glitches, restores the achievement progress for most people, and introduces a host of other tweaks and fixes.
The patch was actually released for the PC version back in October, so these fixes are already in place.
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.Anyone planning on firing this one up now to wrap up some achievements?