Kiddushin 46: The Amoraim Don't Understand the Mishnah!

A new mishnah: a betrothal via a date (the fruit). But is it worth a perutah? Can the value of the individual dates accrue? What if she eats them as he gives them to her? How are we to make sense of this mishnah? Also, a gift to a sister is obviously collateral, a deposit. Why would he say "kiddushin" (in this case)? How did the sanctity of a kohen's food make a difference? What about the challah that is given as flour? How complicated can that flour be whether it's challah or not? Won't it get mixed up? What does the kohen know about whether he can separate the challah from that new dough? Doesn't everyone need to pay attention to these details?