The Septuagint's version of Jeremiah is one eighth shorter than the Masoretic Text's version. In the Dead Sea Scrolls is evidence of both versions.
Did any ancient Jewish writers (such as in the Mishnah, Talmud or Midrash) address the origin of the different source texts or offer an explanation for them?
Secondly, AFAIK the sect that produced the DSS was not the Perushim, and the scrolls were likely not known to anyone after the churban Beis Sheini era until whenever they were discovered in the 20th century.
Ergo, I highly doubt any of the post Bar-Kochba sages ever discussed these issues.
– warz3 Apr 02 '15 at 17:05