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Anakin v Obi-Wan duel over Pace Of Training?

From the OS databank under Darth Vader:

Skywalker was seduced by the dark side of the Force. Fueled by rage and discontent with the pace of Obi-Wan's training, Anakin challenged his master to a duel. Despite newfound power bestowed by the dark side of the Force, which added to his already formidable abilities, Anakin was grievously wounded in the fight. His burning anger kept him alive, and he was forever scarred not only by his wounds but also by betrayal.

Whats that all about?
Discontent with the pace of his training, at that point in the film I wouldnt have thought Anakin felt he had much left to learn.

I think they cite the speed of training because that was Anakin's major issue in AotC. We've seen that and they're trying not to give much away for RotS. Anakin is a Jedi Knight in RotS anyway, Obi-Wan isn't his master anymore.