You bought a domain, then it parks at the Registrar using his name-servers (and while giving a joyful "I PURCHASED LOGGER %name%"). Normally the Registrar allows to use his nameservers associated. If the domain is bought say tonight, it is not instantly (well, I have a logger like this) it becomes yours, because "something" else is happening there (I don't know this). For example, I just bought a few domains that pass the day(or all weekend) as long as lasts the delegation of the domain, then I can either change the nameservers associated with your own, or modify the zone on the name server of the Registrar. Or because your domain has not yet (not fully processed the request) or not at all yours, and you do a malicious attacker :)