I have been puzzling about a certain issue in the Avi Ezri of Rav Shach [in the only law in Laws of Shekalim that there is a chapter in the Avi Ezri]. It is this in the Rambam there is this approach to tithe of animals [every tenth animal must be given away]. It comes into the domain of inheritors it is is not obligated. [That is where is disagrees with the Raavad.] But in the domain --i.e. what is born the the domain of the inheritors is obligated [That is both to the Raavad and Rambam.] The question Rav Shach has on this Rambam is a different. The question is based on the fact that if the inheritors divide and then rejoin, they are not obligated in the tithe. Rav Shach asks would it not be more of a "chidush" [new idea] to say that the inheritors that divide are obligated if the Mishna is coming to tell us יש ברירה [what is divided reveals what was already divided in potential in the past.].
The lack of understanding on my part is this. The mishna certainly holds just dividing changes nothing. The brothers are still obligated in what was born while they were joined. It is the rejoining that makes them not obligated. Clearly Rav Shach here is understanding the Rambam that that mishna is coming to tell us something about there is "braira" יש ברירה or there is not braira [choosing]. But one way or the other does not seem to say anything about if the brothers simply divide.
On one hand I can see the point of Rav Shach. In the way of the Rambam, that mishna has to go according to the opinion יש ברירה [there is choosing]. For if not [that is if the law would be אין ברירה], then when the brothers divide they would be considered as buyers who would not be obligated in the animal tithe. Still it is hard to say that even according to אין ברירה that the obligation they already had of giving every tenth animal would disappear.
I think you can see what I mean. The normal way we understand that people that buyers are not obligated in the maasar for animals is that there is a change in domain--from one person to another. But here animals that were born when the brothers were together are now owned by just one or the other. That is not really a change in domain.
