Rav Huna rules 'Ta'am Eino Mekadesh', meaning that once a person has eaten on Friday night, he no longer recites Kidush until the following morning before eating. The reason for this is presumably, because Kidush is supposed to precede the meal ('Kidush be'Makom Se'udah'). On the other hand, he holds 'Ta'am Mavdil', which means that he is permitted to recite Havdalah even after having eaten. The Chachamim, the Rashbam explains, were simply not so strict regarding Havdalah (either because it is only mi'de'Rabbanan, whereas Kidush is min ha'Torah, or perhaps because Havdalah was not instituted specifically before eating).

The above is based on the explanation of the Rashbam and Tosfos. According to the Maharam Chalavah (citing the Ra'avad) however, what Rav Huna means is that the Chachamim penalized the person who ate, forbidding him to recite Kidush himself (obligating him to hear it from somebody else). And the reason for this is because he showed disrespect for the Mitzvah by eating first, though they did not do so with regard to Havdalah (presumably for one of the reasons mentioned above).

A third possible explanation for 'Ta'am Eino Mekadesh', is that the Chachamim fixed Kidush specifically before eating, and that a person who eats first has lost the Mitzvah altogether. The Rambam may well learn like this, though I am not sure whether he actually does.

In any event, the Gemara concludes 'Ta'am Mekadesh, Ta'am Mavdil', in which case somebody who does eat first (even if he does so intentionally), is permitted to recite both Kidush and Havdalah (respectively) himself, even immediately after his meal.

Be'Virchas Kol Tuv

Eliezer Chrysler.