Romans 11:6 (traditional text)
επει η χαρις ουκετι γινεται χαρις
ει δε εξ εργων ουκετι εστιν χαρις
επει το εργον ουκετι εστιν εργον
but if by grace, not then from works,
else the grace no more becomes grace;
but if from works, not then is it grace,
else the work no more is work.
INCLUDE LINE: א(corr) (B) ψ 88 104 181 330 436 451 614 1241 (1962) 1984 1985 2492 (2495) Byz Maj (Majority of MSS) Lect. Syr-P/H, (Aeth) Chrysost. Theodor. Gennad. Ps-Oecumenius Theophyl.
OMIT: p46 א* A C D G P (81) 629 630 1739 1881 it-ar/d/dem/d/f/g/x/s Vg Cop-Sa/Bo Arm Origen(Lat) Ambrosiast. Chrysos(comm) Theod (comm) John-Damasc.
Paul's long argument borders on repetition, because of its completeness. This is something that often happens in writing as opposed to speaking. A letter affords a chance to be thorough.
The repeating vocabulary also creates plenty of cross-eyes while copying. It is understandable that many a scribe did not fully understand the complex arguments of Paul, and so both lines appear extremely close in both content and meaning. Only careful reading makes the complimentarity of both sentences plain.
But such precise but longwinded arguments become a fertile ground for haplography errors, as in this case. At the same time, it is possible that an Alexandrian editor felt the repetition of ideas was indeed redundant, and has sought to improve the situation by excision (possibly after the variant first appeared).
Remarkable here is that this error appears to have flooded the Latin stream of transmission, and swept the old uncials under its influence too. Nonetheless, the Greek MSS support for the line is overwhelming.
All critical editors follow the Ancient Alexandrian/Caesarean tradition of prefering the shorter text, and the modern versions follow, without explanations.