Wow. Very curious. I hope to get an explanation from our admins about this.
I recall something similar happened in the old CPF years ago. Willets Point, who had admin privileges at the time, decided to leave the forum and deleted his profile. That created a big mess that I had to go behind the scenes to fix. Every thread that he had posted in became invisible. It took me a while to figure out what had happened and ultimately I had to recreate his profile.
Do we have the ability to delete our profiles here? (I'll have to see if there's an option. If I find it, I won't, of course, be able to test it.) If so, that's not a good thing. Obviously, people should have the ability to exit the forum, but it shouldn't have this kind of an impact.