Hardly. That's usually the case of a diplomat working its magic. To cure that, send you assassins on some search and destroy missions. It took a bit of hunting but after a while I finally managed to kill the right diplomats such that things like Rhodes and Crete got taken over by various and sundry powers. Though such vigilance can be annoying as the AI will spam diplomats every now and then, making it quite a b**** to kepp them away from the appropriate factions.