My guild had two members who said this happened. One member clicked Join again and was placed in the TW, the other one didn't check until after the Setup Phase started, so he missed it.
The player who missed - I never saw his name on the "joined" listing, and I was checking the list pretty religiously. We had 0 members who were on the list that were expelled upon switching to the Setup Phase.
I conclude that while it might be dropping "joins", it's dropping them right after players join, so if players just verify that their name is on the list after clicking "join", and check again before it starts - they will be in the TW.
