I got the impression by that ad he cut and the reversal of endorsement that he was personally insulted by being lied to like that. Like Rand showed he has felt about those lies in the last debate. And it makes sense, if you are truly pro-life because you think an abortion is murder, then having somebody say you are pro-choice is the equivalent of saying you approve of murder or other violent crimes and that is insulting, not just politics.
It sounds to me that the people that lied to Dobson exposed themselves as people that use pro-life as a campaign-tactic/plank and not because they are truly opposed to abortion.