When Yom Tov occurs close to Shabbos, whether before or after; and similarly two days of Yom Tov in Chutz LaAretz - according to the opinion that the two days are considered one long day, if he asked on the first day, he may eat on the second day; according to the opinion that they are considered two separate days, he may not eat.

Rebuttal: Even according to that second opinion, he may still eat - the reason that the Mishnah taught that he may no longer eat after Shabbos is because he is able to tithe - but since in these cases he's not permitted to tithe, he may continue to eat. And we have a Baraisa that taught - if he asked him on Yom Tov, he may also eat on Shabbos; if he asked him on Shabbos, he may also eat on Yom Tov.

(R. Yona citing R. Zeira): It refers to fruits that he had in mind before Shabbos, but for fruits that he had not, they didn't allow it.

(R. Mana): The words of the Chachamim support my father R. Yona - as it taught in the next Mishnah - One who imposed a vow on his friend to eat with him, but the friend does not trust him concerning separating Maaser [he may only eat with him for one Shabbos and only if the host told him that the fruits are tithed].

(R. Yannai citing R. Yishmael citing R. Yochanan): When they permitted the first Shabbos, it was referring to Shabbos Sheva Berachos (the first Shabbos of their marriage) - and they permitted it to avoid animosity (that might be caused if one party wouldn't eat the food of the other party). He did not have the fruits in mind before Shabbos, but they nevertheless permitted them to avoid animosity. (This is a proof for R. Zeira above (c).)

If he was invited for that first Shabbos but he didn't come, on the second Shabbos, he may not eat until he tithes or asks about their status.

Question: Didn't he ask already?

Answer (R. Yona): Then, he asked himself; but now, (on the second Shabbos) others asked for him.

Question (R. Yona): How could he ask him (without causing him to be angry)?

Answer: In an indirect fashion.

R. Yona follows his reasoning elsewhere - R. Yona bought wheat from a villager (and forgot to tithe them and remembered on Shabbos) - R. Yona went to the villager and said, "It's not that I suspect you of (intentionally) not tithing, but when I came to you to buy wheat, I saw so many people that I said to myself that perhaps you are so busy, you forgot to tithe''. The seller answered that the wheat was tithed. R. Yona didn't rely on him and continued to question him. The seller said, "Why do you suspect me? I already told you that I tithed them!''