That phrase does appear to be an "imperfection" (as it is called) which existed in the original text. And in fact, it was quite difficult to take back words that were already written—so difficult, perhaps, that they decided to re-state the entire idea correctly.
According to LDS Church history, The Book of Mormon has unique origins as a volume of scripture. Like the Bible, its words were inspired by God. Unlike the Bible, its words were translated/copied only once, directly from the original document, which, in the case of The Book of Mormon, was a codex of golden plates. Instead of being written on papyrus or a typical form of "paper," these plates were metal, and so it was difficult to engrave writings on them.
So why write on metal plates? Because it was a commandment, and because the properties of metal ensure longevity.
Even though it was difficult to engrave writings on them...
1 Now behold, it came to pass that I, Jacob, having ministered much unto my people in word, (and I cannot write but a little of my words, because of the difficulty of engraving our words upon plates) and we know that the things which we write upon plates must remain;
... it was important to them that the plates were metal and could be preserved for generations:
4 For it were not possible that our father, Lehi, could have remembered all these things, to have taught them to his children, except it were for the help of these plates; for he having been taught in the language of the Egyptians therefore he could read these engravings, and teach them to his children, that thereby they could teach them to their children, and so fulfilling the commandments of God, even down to this present time.
Moroni was the last steward of The Book of Mormon. His father Mormon abridged most of the text. Moroni explains their difficulty in Mormon 9:
30 Behold, I speak unto you as though I spake from the dead; for I
know that ye shall have my words.
31 Condemn me not because of mine imperfection, neither my father,
because of his imperfection, neither them who have written before him;
but rather give thanks unto God that he hath made manifest unto you
our imperfections, that ye may learn to be more wise than we have
32 And now, behold, we have written this record according to our
knowledge, in the characters which are called among us the reformed
Egyptian, being handed down and altered by us, according to our manner
33 And if our plates had been sufficiently large we should have
written in Hebrew; but the Hebrew hath been altered by us also; and if
we could have written in Hebrew, behold, ye would have had no
imperfection in our record.
34 But the Lord knoweth the things which we have written, and also
that none other people knoweth our language; and because that none
other people knoweth our language, therefore he hath prepared means
for the interpretation thereof.
... and in the previous chapter:
12 And whoso receiveth this record, and shall not condemn it because
of the imperfections which are in it, the same shall know of greater
things than these. Behold, I am Moroni; and were it possible, I would
make all things known unto you. ...
17 And if there be faults they be the faults of a man. But behold, we
know no fault; nevertheless God knoweth all things; therefore, he that
condemneth, let him be aware lest he shall be in danger of hell fire.
...and on the title page:
And now, if there are faults they are the mistakes of men; wherefore,
condemn not the things of God, that ye may be found spotless at the
judgment-seat of Christ.
Basically, the authors knew they had faults, and it was easier to re-state the idea correctly than it was to hammer out the engraving to overwrite it. It also seems, from all the passages about their weakness in writing (I haven't shown all of them here) that it was necessary for there to be some minor flaws in the text. (Discovering the purpose for that is left as an exercise for the reader.)
I don't know of similar passages in the Bible, for whatever reason (if anyone can find some, I'd be interested to see). The Book of Mormon actually indicates that the first several books of the Bible were written on metal/brass plates which Lehi took with them across the sea, but the earliest Biblical manuscripts we have aren't engraved on metal (that I know, at least), so it may not have been difficult to overwrite and change the text.