I reskinned a player head (my alt Vardogr) but it only intermittently shows the new skin and mostly reverts to the previous skin. Does anyone know where this is sourced from? Is this in a local cache? Is there some way to force it to change to the new skin?
Nope. Since the change to UUIDs in 1.7.9, heads retain the same skin as they had when the person got slaughtered.