But first of all I must tell you that Sirius's will was discovered a week ago and that he left you everything he owned." ...
"This is, in the main, fairly straightforward," Dumbledore went on. "You add a reasonable amount of gold to your account at Gringotts, and you inherit all of Sirius's personal possessions. The slightly problematic part of the legacy —" (HBP)
It says "to your account" - does that mean it was moved from Sirius Black's vault to Harry's? That's what the Lexicon says but I think the word "account" makes that less certain.
All the other discussions of family vaults (Lestranges') imply that they belong to the family line - does that mean that other Blacks (Narcissa/Bellatrix) would inherit the Sirius' vault? Or would Harry? Or would the vault revert to Gringotts, sans the contents that are moved to Harry's vault?