I thought I had the permissions set up properly so that newly-registered Mando'ade could not post anywhere but the Welcome Thread. I was wrong. In order to further protect ourselves from spambots and the like, I have revised the permissions such that first-time posters may only post to the Welcome Thread (and when they do so, it will require me to approve their post). Once I approve that first post, that user will be able to post anywhere else in the forum, as usual. This does not affect existing users, only newly-registered ones.
I apologize for whatever inconvenience this may cause, but it makes it easier for me to catch a spambot before they post, and I thought it had been set up this way (excluding post approval) all along. *facepalm*