Some scenes almost look to have a rubber stunt helmet of some kind, like they forgot to swap it out. The Jango twirl being one of these, though I could be totally off base here. There's definitely something weird going on with it, but like others say above both exist.
Story wise it appears the dent is intended to be from headbutting Kenobi during the Kamino fight, but the screw up and weirdly show a CGI scene before it with the dent already there a little before that.
Interested to see the dented jangos ya guys come up with, those should be cool