That's the latest buzz at AVS Forum, where poster PFC5 has posted this image of the mystery 1.3 update. However due to server problems it hasn't been distributed to very many others and we still don't know what it does, if anything. The original poster originally had a problem with his Toshiba displaying an RCA splashscreen, so that may be the only difference between this and the official 1.2 update now available for download. Otherwise, there's not much to say at the moment until early adopters get their hands on it and try it out.
Oddly, contrary to some reactions around the net regarding updates and bugfixes becoming commonplace in consumer electronics, many posters in the thread are encouraged by the indication Toshiba will provide frequent updates for issues discovered by the community. This isn't that surprising when you think back to the many problems early adopters often have to deal with without an official response or fix (anyone remember many of the early DVD players? Ouch.)