I'm running 10.8.5 and installed some of the newer text-to-speech voices, including "Samantha" (aka Siri), "Tom", and "Jill". They work fine, except for the word "seq":
say -v Jill seq
produces the spoken words: "the following".
say -v Samantha "consider seq question"
produces the spoken words: "consider the following question".
I tried the above test on each of the voices I have installed, and only "Samantha", "Tom", and "Jill" exhibit this behavior.
I haven't found any other words that produce wrong output, but there may be more.