The sources and discussions on this issue are there for those that want to find them. I vaguely remembered the Gemara and found the following just by googling:
Start with the Gemara in Sanhedrin 21b – 22a – a three way machloket about which was the original script and how/why it was changed.
The Rishonim also discuss it on the spot. There is discussion of the issue in Sefer Ikarim (maamar 3), Meshech Chochma (in devarim 31:9), Maharal (tifferet yisrael), Torah Temima (devarim 17, nt 92) as well.
