Rav Shach brings two arguments of Rav Akiva Eiger and and asks on both arguments. This is in the Correspondence of R Akiva Eiger letter 23.
[The issue is also brought in the Shulchan Aruch of Rav Joseph Karo in the commentaries].
The case is this. Hamez [yeast or leavened bread] belongs to a gentile that is in the domain of a Israeli, and the Israeli has accepted responsibility and an obligation to pay for it if it is lost or stolen. He can not keep it on Passover. But let's say he did not get rid of it and kept it on Passover. After Passover is it allowed or not to derive benefit from it?
The Yerushalmi [The Jerusalem Talmud] brings two opinions about this. One forbids and the other allows.
The Rambam states the law as the opinion that it is forbidden. Why? It is a law of the sages and any law of the sages we always go by the lenient opinion. Rav Akiva Eiger wants to answer this.
One answer if based on the Mishna: One stole hamez and it was still in his possession on Passover. After Passover he wants to return it to the owner. He can say (הרי שלך לפניך) "What you own, you can now take."
One way to explain this is that it is not forbidden to derive benefit from the hamez. [The reason is on whom would the law of the sages apply to? Not the person that was the victim of the theft. But not the thief either since even if it would be forbidden he could still say "what you onw now you can take."]
So the law that hamez that Passover has passed over on is forbidden would not apply. This explanation of the Mishna would be like the opinion in the Yerushalmi that hamez of a gentile in the domain of a Israeli is permitted after Passover. But since we see that our Gemara [Pesachim 105] holds the explanation of the Mishna is that even though the hamez is forbidden in use so we do not go with the lenient opinion of the Yerushalmi.
One question I have on Rav Akiva Eigger. is the very idea in itself { even if it would be forbidden the thief could still say "what you onw now you can take."] This is sort of hard to see since the whole question in the first place is is it forbidden? Presumably this opinion would hold that if teh hamez is forbidden in use then the thief could not say this.
But that is not the question of Rav Shach. Rav Shach simply brings two Gemaras in Pesachim that show that the explanation of the Mishna is not in question. The hamez is forbidden.
