First an opinion. I think the Registrar did an excellent job. I have no criticism whatsoever to make of him. I also believe that the information that was given to him was correct information.
Next the facts
1) Only one person's name appears in the 1840 box entitled "Signature, description and residence of informant".
2) The surname of the person in that box is Masters.
3) The full name in that box is Ann Masters.
4) On 30 March 1843 Ann gives her surname as Masters.