Es sind Updates für LEFT 4 DEAD 2 und ALIEN SWARM erschienen. Besonders bei LEFT 4 DEAD 2 hat man später einen Fix im Versus-Mode nachgeschoben.
Die genauen Fixes sind folgende:

LEFT 4 DEAD 2

• Encore mutation: Versus Survival (PC), Four Swordsmen of the Apocalypse (Xbox 360)
• Added a setup timer to Versus Survival
• Fixed an exploit that dropped players from dedicated servers
• Fixed bug in Versus-Survival where a team could get 5 survivors

ALIEN SWARM

• Fixed XP/Level transferring to a new player using an old player’s PC
• Addon VPKs get priority over base VPKs
• Added -override_vpk command line option to make loose files have priority over VPKs
• Stopped spawners shutting down completely when an alien is blocking the location for more than 5 ticks in a row.

Quelle: STEAMPOWERED.COM