.כָּנְסָה וּפָשְׂתָה, פָּשְׂתָה וְכָנְסָה, רַבִּי עֲקִיבָא מְטַמֵּא
If it contracted and [then] expanded , or expanded and [then] contracted, Rabbi Akiva calls it impure.
בַּהֶרֶת כַּגְּרִיס וּפָשְׂתָה כַחֲצִי גְרִיס, וְהָלַךְ מִן הָאוֹם כַּחֲצִי גְרִיס, רַבִּי עֲקִיבָא אוֹמֵר, תֵּרָאֶה בַתְּחִלָּה.
A Baheret like [the size of] a bean that expands [the size of another] half a bean but the original [Nega area] is diminished by half a bean, Rabbi Akiva says: It should be seen as if it was the first [time].
This seems like a contradiction.
Isn't Mishnah 8 also discussing a case of expanding and contracting (although granted in a different direction)? Why here does R. Akiva rule that the nega' is seen as if it is new? Doesn't this contradict his ruling in the previous mishnah that in such a case the nega' is definitively ruled impure?
What rule is R. Akiva proposing in Mishnah 7, and why does it not apply to the case in Mishnah 8?