darth_ender said:

I had a thought that I bet most will disagree with: Vader should refer to Palpatine as Master Sidious at least once in ROTJ. There, I said it!

I have mixed feelings about that. It would be good for the sake of continuity, I suppose, but I'm personally the type who thinks that we should try our best to make the PT fit the OT and not the other way around. That being said, I AM pretty big on continuity... perhaps it might be better, though, to remove all instances of the name "Darth Sidious" from the PT films and therefore remove any reason for Vader to refer to him as such.