R. Akiva's opinion regarding tzara'at that expands and contracts (Nega'im 4:7-8)

Question

Nega'im 4:7:

.כָּנְסָה וּפָשְׂתָה, פָּשְׂתָה וְכָנְסָה, רַבִּי עֲקִיבָא מְטַמֵּא‏

If it contracted and [then] expanded , or expanded and [then] contracted, Rabbi Akiva calls it impure.

Nega'im 4:8

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?

Answer 1

According to the Bartenura, in Mishna 8 the baheret only "moved from West to Est" without changing size. The change of place can be seen as if the first Nega disappeared and a second, new baheret appeared and this new Nega needs Hesger.

In the Mishna 7, it did shrink and widen. Rabbi Akiva sees this event as an expansion of the same Nega. So it's muchlat. Because the center of the baheret didn't move, it is the same Baheret.