I'm not sure when the thought that this discrepancy in Gen 4:18 might be an a error first occured to me. Probably, I was a teenager fresh from reading The Promise, Potok's account of an Orthodox rabinical student's effort to reconcile the outside world with the world of halacha.
From time to time, I've stumbled across other evidence that some of the Torah was muddled during the long years of handwritten transmission. Like Potok's character I've struggled to reconcile this information with the halachic reality, and the theological insistance that this absolutely could not have occured.
I'm not alone. Here, for example, is Menachem Cohen, Professor of Bible at Bar-Ilan University, discussing how a religious community should deal with textual discrepancies:
Gen. 46:13 reads: "And the sons of Issacar are Tola and Puah and Yov and Shomron." The third name on the list, Yov arouses some doubt as to its accuracy, in light of the following: In Num.26:24 the name is given as "Yashuv"; In the Samaritan version of the verse in Genesis, as well as in the Septuagint, the name is Yashuv; I Chron.7:6 in the MT reads: "And the children of Issacar are Tola and Puah, Yashiv (Qere: Yashuv) and Shomron, four sons." These facts lead us to the conclusion that Issachar's son was indeed called Yashuv, and that Yov is an error which crept in to the transmission of the MT before sanctified status was granted to its consonantal base. A modern religious commentary will not have fulfilled its obligation to its readers if it did not bring these facts and their like to their attention. Nevertheless, the historical conclusion is to be kept separate from the question of writing a Sefer Torah. Since the spelling has been sanctified together with the sanctification of the Authorized Text of the MT, anyone who changes one letter of this word invalidates the Torah scroll, as only this spelling has validity and carries halakhic weight when writing a Sefer Torah.The discrepancy, in Professor Cohen's view is an error, but an error that has been institutionalized; as a result we're stuck with it.
I find his line of thinking appealing. It's sensible, honest, and respects both halacha and reality.
BUT IS IT KEFIRAH?
No. It's well-established that many of our Sages were of the opinion that our Torah is not a letter-for-letter match with the Torah Moshe received at Sinai. Furthermore, it's also well known that the Rambam's famous declaration that the Torah was unchanged was part of a polemic response to Muslim claims that Jews had edited out the story of God's permanent rejection fo the Jewish people following the Golden Calf episode.
I know it won't be easy for some of you to accept what I've said about the Rambam, but consider this: Rambam was a Rishon, not God, and not Moshe Rabbeinu. I don't know, how his ikkarim managed to cause so much irrational, obsessive-compulsive behavior, when some of them were contextual polemics, and when they were the opinion of just one man. Other Rishonim disagreed with him heartily, and some of his works were burned by other Rishonim! Was everyone on the anti-Maimonidean side of the controversy a kofer? And did they all accept the Ikkarim, blindly and unflinchingly?
Furthermore, were the baalei haTosfot kofrim? They were well aware of transmission errors, said so explicitly and called attention to them!