I’m a professional sign-language interpreter, and as such have a bit of a professional interest in all things pertaining to Deafness. I also have lots of Deaf friends and clients, and CC is one of their favorite pet peeves.
Often, the “live” captioning on the news, etc, is LIVE–in other words, some hapless person is sitting at a keyboard, trying to keep up to the spoken words. Since people speak at a much more rapid pace than most folks can type, I can see how this would create a problem. I don’t know what kind of keyboard is used–I would hope that an arrangement like a court reporter’s would be employed–but a person who WAS a court reporter, and is now an interpreter colleague of mine, says that the court thingy records how things SOUND, and must by typed on a regular keyboard later, to be legible. This would account for the homonym problem.
As for the &^ odd symbols, etc, I suspect it IS a transmission problem. Many TTYs (also know as TDDs or Telephone Devices for the Deaf) have similar problems to CC. For some reason, due to internal or environmental factors (loose wire/lots of background noise) they will produce gibberish on random occasions. This can be quite annoying, as phone conversations look like this:
SO, CAN YOU WORK FOR ME ON %&^E^$ %&^^((&^ AT (^G(I(* O’CLOCK?
Just my two cents.