MDD and rabbiofberlin,
First of all, I don’t think that R’Moshe argues on what I wrote. And MDD is correct that it is possible to have a case where it is absolutely clear (“anan sehadi”) that the kabbolas mitzvos does not have actual intent. However, it is hard to imagine an Orthodox Rabbi performing the conversion in such a case.
So for example, if a man is converting for marriage and he says to his fiancee and the rabbi, “I don’t mind going through the whole ritual and stuff but I am not binding myself to any sort of code of conduct for the future.” That would be pretty clear that later kabbolas mitzvos is not valid (absent a retraction of his earlier statement). Similarly, I could hear an argument that if he crossed his fingers as he dunked in the mikvah, it would not be valid.
The point is that for there to be an anan sehadi, the purported ger must have done some maaseh or made some statement that made it absolutely clear that he did not mean to be mekabal the ol of the mitzvos.
We can safely assume, however, that if talmidei chachamim oversaw the conversion, there was no such anan sehadi and the conversion is completely valid.