In a previous question it has been asked (or should it be "it was asked"?) whether "He is demanding my father to pay him $600" were (or should it be "is", or, perhaps "was"?) correct or not, but @kiamlaluno objected that the grammatical version of the above sentence is, or would be, "He is demanding that my father pays him $600".
Please, note the italicized pays, which, I think, kiamlaluno aseptically used in reference to the third person "father".
Answering the question, another user, @Jay, presumably a native speaker, wrote 'a more common wording would be [...] "He is demanding that my father pay him $600"'.
Being an Italian speaker, and, as such, particularly aware about the difference between "indicative" and "subjunctive" moods, I don't think Jay randomly used "pay" rather than "pays", as Kiamlaluno did.
So, I think that "pay" is correctly used in the subjunctive form there, whereas "pays" is wrong because it doesn't render the involved meanig of the sentence.
Am I wrong in asserting what above? If so, why?