In one of the later chapters, it's revealed that the reason the Death Eaters were able to track the trio to Tottenham Court Road so soon after they Apparated there on escaping from the wedding is that one of them said the name "Voldemort", which has been made Taboo so that the Death Eaters can instantly trace anyone who utters it to where they were, even through the most powerful concealment spells possible. (Hence why they were later tracked to their tent and captured, despite use of such spells to hide the tent.)

Yet whilst they are at 12 Grimmauld Place, which is likewise protected (by the Fidelius Charm as well), "Voldemort" is said several times by Harry or Hermione. Why doesn't the Taboo betray them there?