It is almost impossible in an official film and television program usually, except that the subtitles are mistyped, or that the foul words are not shown or replaced with the homophones intentionally. But, occasionally I also discover the cases like you said in TV drama subtitles, such as typos, mistyped synonyms. However, subtitles do not match the subtitle is common in some unofficial subtitles, especially for non-Mandarin movies, like English or Cantonese movie, for there may be multiple versions from different netizen translation group. Even, there are more than one official translation sometime, for example, I bought a Chinese version DVD of the movie Inception before, I also watched the Blu-ray version later, the translations are different from each other.