Wed Gitten 10

The tana Kama holds that someone can be Yoitzeh eating Matzos from a Kusi, since Matzos are written in the Torah.

Tosfos explain two conditions to make this true. We have a Halacha that bread of a Kusi is forbidden. So to make these Matzos Kosher, we must say that the dough belong to a regular Jew and the Kusi just baked it. That's why it doesn't have the Halacha of Pas Kusi.

Another condition is, we must know that the Kusi hadn''t prepared any other Matzah for himself. If he did, then perhaps the other one he reserved for himself. This one, since he's not using it himself for the Mitzvah, so he maybe didn't make it L'Shma. Although he's causing others not to be Yoitzeh, that's not a problem for the Kusi, since he doesn't believe that's the explanation of the prohibition of Lifnai Ivar Lo Sitein Michshal.