I'm an administrator (not the technical backroom boy) for a forum and I have to say after playing on forums as a user for a long time Xenforo is fantastic!
We have an issue in that whenever a post is created in MS Word and the copy and pasted to a message in a thread the system gives and error. I think the issue is related to hidden characters...
We also can't use special characters in the messages either and I guess it's the same issue?
I have tested copy and past here as well as special characters and it has been accepted no problem?
Test - Ω - Yes it works!