I still don't know what the hell is going on here. There doesn't seem to be any rhyme or reason as to why they are disappearing. I can only assume that it's because they aren't being made through the forum directly and are coming from the website, but I don't know precisely why. Especially considering the threads seem to be CREATED just fine, and are disappearing later. I simply don't know what's going on, but I'm continuing to investigate.
Edit: OK, I've made a small change to the Forum software. I'd appreciate it if you'd all keep an eye and let us know if any other TalkBack threads disappear.