Is there an obligation to have melave d'malka on Motzei Shabbos which falls on Yom Tov?
Although there is anyways an obligation to have a Yom Tov meal, there are still some possible ramifications:
Melave D'Malka for women who are makpid on Melave DMalka, but according to many poskim are not obligated in Seudas Yom Tov (see Shu"t R' Akiva Eiger §1).
Should one add an extra food item for Melava DMalka? (Similar to the ruling of the Mishne Beruro (419.2) writes that when Rosh Chodesh falls on Shabbos, 'medakdekim' should add an extra food item to be recognizably lkovod Rosh Chodesh.)
Does one need to have specific intent when eating the Yom Tov seuda to discharge his obligation for Melave D'Malka? Although Melave Dmalka generally does not require specific intent [For two reasons: 1) We pasken that mitzvos drabbanan ein tzrichos kevana (intent is not required), 2) According to many poskim mitzvos shel achila einon tzrichos kevana], the Rishonim say that when one has specific intent for one obligation, that automatically constitutes kavana hefchis (intent NOT to discharge) for any other obligation. Therefore, when one eats Seudas Yom Tov, one will not be yotzei melava dmalka unless he has specific intent.