Good to know that you cut entirely GI from your edit, CaptainFaraday. I was looking for an edit that make exactly that, since he is basically useless in the story and his makeup is terrible.
(I know you can say that part of Anakin was disappointed in the battle, and or felt sorry for him. Or maybe just repaired Obi Wan for leaving him after he got burned. So he let him escape, but at that scene it didn’t really land that well.)
Yeah, this is why I suggested earlier that the Palpatine scene could take place just after the first Vader vs Obi-Wan battle. Palpatine imply that Vader could still be attached to his master, and this would be the reason why Vader let him walk out. If you think of it, this conversation made much more sense after the fist battle than after the second battle, since in the second one, Vader looks much more obstinate to kill Obi-Wan, and in the first duel Vader seems to have more grief and the will to make Obi-Wan suffer, but not kill.
Of course that this would require some flashback to occur while Vader observes the flames or while the robot rescues Obi-Wan. That’s not a perfect solution either, but is a plausible reason, for me at least. Anyway, is really hard to think in a logical reason for why Vader let Ben go in that moment.