The dutch mechanic on the team already told the story back in 2009.
Basically, on the Restefonde while everyone was at their limit, Sastre felt great and wanted to attack. He asked Riis, who said "ask Frank", since Frank was in yellow. So he asked Frank...
Frank said no, Sastre just followed wheels all day. Riis went up to Frank and yelled at him that if he wanted to win the Tour, "it has to hurt and it has to hurt NOW" and Frank replied that he couldn't do it. Frank's a damned nice guy, but he doesn't seem to have the mental fortitude required, sadly.
Then at the end of the Tour Andy complained that Sastre worked against Frank.
Personally, I lost all respect I had for Andy back in 2009 the moment he randomly quipped that Moncoutié "is *** in the head" apropos of absolutely nothing. If only he was a nice guy like his brother...