The exchange of dialogue between Obiwan and Vader on Mustafar was not right for the stitution. They spent practically everyday together for years and the way Vader speaks to him seems to show that there were serious problems in their relationship. But that can't be true can it? In AOTC Anakin says he thinks of OB as a father. They were very close and when there about to do battle, all Vader says is an insincere "don't make me kill you" I just would have expected on Mustafar that what was happing would trancend their differences in their relationship and Vader would be honest about the whole stitution. Instead he tries to throw the "Jedi are plotting to take over" thing out there and "the Jedi are evil".