If they do this unintentionally and (almost) all the time, then I believe this may be a sign of one of the various types of autism - possibly Aspergers. I think I have something similar, where I misunderstand what's being said because I cannot adjust my interpretation to the context, then get into an argument about whether someone failed to express themselves clearly. On the other hand it could just be someone under pressure who hasn't learned how to defend themselves confidently yet.