I don't have any visual documentation for this. I hope I can explain it clearly. Also not sure if this was brought to your attention before.
I've noticed this several times before, and again yesterday afternoon. In the "Most recent tagged threads", the RAW icon for the August 1 show thread appeared twice side by side. Hovering over and clicking both icons confirmed they linked to the same thread. At the time, the most recent post was Justin's. (The W) But directly below his post was an empty post from him that said "deleted by JustinShapiro".
The double icon eventually disappeared, along with Justin's empty post. But I don't know when that happened (maybe when emma made her post?).
It's probably keyed to the fact that those double posts probably have the same timestamp and the "last post in the thread" code doesn't check for that when it's sorting last post(s) in threads, so it handles it kinda not so gracefully. I am too lazy to fix it.
Hmm... I tested on pieman and DEAN in the test folder and it worked after I included a closing font tag at the top of my header ('twas missing), but it didn't work here until I placed a closing font tag before the end of your quote. Interesting.