Ma'aser sheni mamon gavoha and achilas matzah

The gemara (pesachim 38a) writes that whether one may use matzah made of ma'aser sheni depends on the machlokes Rabbi Meir and the Chachamim that appears in many places whether ma'aser sheni is mamon gavoha or mamon hedyot. The Rambam (chu"m 6:8) paskens that matzah of ma'aser sheni can be used in yerushalayim but not outside (gevulin). The Lechem Mishne cites a gemara in sanhedrin (112) as the basis for the distinction between Yerushalayim and gevulim, but that distinction assumes that the whole machlokes R"M and the Chachamim is only within Yerushalayim (in gevulin it would be mamon gavoha according to everyone) proper and the Rambam paskens like the Chachamim. The difficulty is that the Rambam clearly writes in hil ma'aser sheni 3:22 that ma'aser sheni mamon gavoha hu, which sounds exactly like R"M, and the Rambam draws no distinction between Yerushalayim and gevulin!
The Rav has a long essay on the machlokes R"M and Chachamim which is a work of art (see Koveitz Chiddushei Torah. In a nutshell: there are 2 aspects to the issue of whether ma'aser sheni is mamon gavoha or mamon hedyot - 1) a question of dinei mamonos: is the ba'alim on this food its owner or hekdesh; 2) a question of issur v'heter: is this money consumable for mundane use or must it be used only for designated purposes. For example: by kiddushei isha, ma'aser sheni is excluded not just because if it is mamon gavoha the mekadeish is not the ba'alim, but because the cheftza shel ma'aser sheni is something that has a kedusha of being nitan for ma'aser and not usable for kiddushin.
By matzah and other dinim that depend on ba'alus - "lachem" (not mecessarily that you own the matzah, which is a seperate discussion, but simply that the matzah be something which has an owner), the Rambam distinguishes between Terushalyim and gevulim. But when it comes to kiddushin and other uses of ma'aser sheni that depend on its being a cheftza shel ma'aser which is nittan only for certain purposes, the Rambam paskens across the board that ma'aser is mamon gavoha. (I don't know if I have done justice to the piece in this one paragraph - it is worth seeing inside).