Sokudo Ningyou said:
The one thing that has bugged me since the EU and prequels established "Darth" as a title, not a name: editing out Obi-Wan's constant use of it during the final duel and replacing it with "Vader." To me, at least, it's a glaring continuity error, and annoying even in context with the other two original movies, as everyone uses "Vader" when not using his full title.
It always seemed to me like a sarcastic use of the title, almost as if he is saying, hey, "Darth", look where that got you.