I have an idea about the problem involving Vader letting Obi-Wan escape in their first duel.

When the robot rescues Obi-Wan, it could show Vader having a flashback of when he rescued Obi-Wan in the Invisible Hand. After the flashback, it shows Vader turning around, leaving Ben. The scene following this would be the one where Vader talks to the Emperor.

This would imply that Vader letting Kenobi go was because he still felt something about his master, even 10 years after the events of ROTS.