... you still control a "Blood Doll" (you played originally) on a vampire that is now controlled by another player (stolen via "Graverobbing" or "Form of Corruption" for example) , even though the player controlling the vampire can use the "Blood Doll" at his own whim (but the later is only because of the Blood Doll's card text).
The point of this scenario is really that you don't loose control of master cards played on a vampire, even if you loose control of that vampire. One important effect of this is that the "Blood Doll" in the example above (or any other master card played on a stolen vampire) is burned as soon as the player who originally played it is ousted. This is in contrast to minion cards like "Disarm" or "Anima Gathering" which are always controlled by the controller of the vampire, and stay on the vampire even if the player originally playing it is ousted.
Reference: VtES Usenet Newsgroup.