Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

General:
-Fixed survivors being able to climb some infected-only ladders

No Mercy 1 Apartments:
-Survivors should no longer be able to fall into the street-level infected-only area from the starting rooftop -Players should no longer be able to drop down onto the invisible brush at the corner.
-Survivors should no longer be able to incapacitate themselves by jumping toward the electric box prop opposite the starting rooftop. It should now be fatal

No Mercy 2 Subway:
-Players should no longer get stuck when in the back corner underneath the starting safe room -Survivors should no longer be able to jump onto the tiny ledge on the side of the building following the door/generator event -Made the piano near the ending safe room into a an immobile, static prop to solve an issue with infected players using it to block the safe room.

No Mercy 3 Sewer:
-Survivors who somehow manage to get on top of the gas station should no longer be able to leave the map.
-The work light at the mid-way point in the sewer is now an immobile, static prop to solve an issue with infected players using it to block survivor progress.

No Mercy 4 Hospital:
-Added the missing "breakable" decals to the breakable wall in the second part of the stairwell.
-Made the breakable wall in the second part of the stairwell breakable to all infected.
-Survivors should no longer be able to enter the infected-only vents and passages above and near the elevator event.
-The two tank-only breakable walls in the upper, under construction floor into can now be broken by any infected.

No Mercy 5 Rooftop:
-Added several props to cover and remove an invincible spot on one of the lower tiers of the rescue rooftop.

Cold Stream 4 Cut-throat Creek:
-Fixed infected not being able to path to survivors when standing in the boat near the tank fight.