Many of the official servers are outdated, as I noticed it said on the opening message (what you see when you hit the "H" key by default) and it leads to at least two problems.
1. Workshop items do not work. For the most part, there's nothing wrong with this happening, vanilla L4D2 is fine.
2. Glitches and bugs which have been fixed by Valve still occur. For example, I just got done with a versus match on Dark Carnival. The ending crescendo for Map 4 never had a horde unless a Survivor was vomitted on by a Boomer. This happened for both teams. Later, at the finale, the chopper arrived early for both teams. These are issues the team at Valve have addressed and fixed, but because the servers are outdated, these fixes are not applied to the servers themselves, at least, that's what I'm speculating.
Just to clarify, not all the official servers are in this shape; most of the time they're fine, with complete Workshop support and everything. In fact, when you start a game (at least from the lobby), if you hear and/or see an advertisement start to play, you're on an outdated server.
Well, that's all. Tell me what you're thoughts are in the comments, and hopefully Valve can work something out soon.