This is how the bug happens:
1. Person tells in chat to /join him for taxi
2. People try to /join on him
3. One person tries to join multiple parties
4. All invites bug out and the game says they are in another party
5. Server becomes full and many people are left out before they can join
This bug has some big consequences for organized world events such as Tequatl and Triple Wurm. Currently large communities and alliances taxi their people into the same server before it becomes full. This is done by inviting people to the party. As people try to join multiple people at once it can cause quite a frustrating situation for many.