The sour grapes syndrome

Whenever anyone resigns from PKR or Pakatan Rakyat they always say it is because they are ex-Umno or ex-Barisan Nasional people; so what do you expect? These people are not reliable or honest and eventually they betray the opposition and go back to their old party. Does this apply to all ex-Umno or ex-BN people in the opposition who are yet to leave the opposition to go back to the ruling party?