Once the group is down to just the contenders, you do not go to the front unless you have something to gain. Frank was pulling the group in support of his Bro. They were putting time into LA, Sastre, Wiggins, etc.
We don't have any idea what AC was thinking when he surged. He may have seen an opportunity to take the stage win and gave it a go. Both Shleks were able to match him so he had to shut it down and rethink that.
It was just unfortunate that Kloden was not able to follow as well. Once isolated, AC had to be defensive and just follow wheels. He went from an attempt to gain time on Andy Shlek to ensuring that he didn't loose time.
When the group was down to four, Kloden was either struggling or saving himself for an attempt at the stage win. He was no longer supporting AC. AC didn't need him for pace-seting so it was ok to drop him.
OTOH, if Kloden was sitting on for the stage win and AC knew it...then AC shafted his teammate. Not cool!