Trading(with NPCs - haven't tested clients yet) causes a crash somewhere. It doesn't shut down the zone that I've seen, but the trade fails and the player loses the item.
After doing some digging around it looks like it's crashing right around:
Code:
parse->Event(EVENT_ITEM, with->GetNPCTypeID(), 0, with, this->CastToMob());
In void Client::FinishTrade(NPC* with) in client.cpp
What's really odd is that I can't find any changes whatsoever relating to parse->Event() that could cause the crash.