>> You're correct that the Luke 4 passage and the Isaiah 61 passage differ. The book from which Jesus read was given to him and He read from it as it was written in it. It is possible that He realized that the passage was not entirely accurate, but He read it anyway as it was written on the page in front of him as He was supposed to do without correcting it. <<
That's desperate. You think he had a stenographer with him? Luke records the Septuagint because that's what LUKE had and/or that's what the Holy Spirit inspired him to record. 300 out of 350 citations in the New Testament use the Septuagint; that's simply one of the longest passages, so the differences are most plain.
>> It appears to have been a tradition in the synagogues to read from the Hebrew text first, then to read the same passage from a Greek text <<
Says who? Or does is this simply conjecture to fit your model? (It would make sense if this were done among the Jews in exile, but it seems bizarre to read Greek to Jews in Palestine unless the Greek were somehow thought to be superior to the Hebrew, like Catholics who would read Latin before their vernacular.)
>> which even Jews of the 1st century BC often criticized as being full of interpolations, paraphrases, and inaccuracies. <<
Which would make it all the more bizarre to cite the Greek, if Jesus also read the Hebrew... unless Luke was deliberately using the Greek for some other reason. That reason is clear: the Septuagint was what was known to first century Christians and exilic Jews whom the Christians hoped to convert.
Incidentally, while I'm sure that Jews of different sects criticized each others' translations (like the King James Only folks, for instance), the name "Septuagint" refers to a legend, very widely believed at the time of Christ, that 70 translators, all working in complete isolation, produced the exact same translation, thus supposedly demonstrating that there was among them a unique gift of inspiration. Christians never asserted the factuality of that notion, but it certainly demonstrates that a sizeable portion of the New Testament's target audience thought very highly of the Septuagint.
Jerome, while accepting the Church's authority on using the canon of the Septuagint, certainly believed the Jews of his day who complained that the Septuagint was filled with translation errors. That is quite unfortunate, because if the congruity of the Greek New Testament and the Greek Old Testament were apparent to the laypeople of the medieval era, Luther's lies wouldn't have been nearly as successful.
"Matthew, also called Levi, apostle and aforetimes publican, composed a gospel of Christ at first published in Judea in Hebrew for the sake of those of the circumcision who believed, but this was afterwards translated into Greek though by what author is uncertain. The Hebrew itself has been preserved until the present day in the library at Caesarea which Pamphilus so diligently gathered. I have also had the opportunity of having the volume described to me by the Nazarenes of Beroea, a city of Syria, who use it. In this it is to be noted that wherever the Evangelist, whether on his own account or in the person of our Lord the Saviour, quotes the testimony of the Old Testament, he does not follow the authority of the translators of the Septuagint but the Hebrew. Wherefore these two forms exist "Out of Egypt have I called my son, " and "for he shall be called a Nazarene" (Jerome. De Viris Illustribus (On Illustrious Men). Excerpted from Nicene and Post-Nicene Fathers, Second Series, Volume 3. Edited by Philip Schaff and Henry Wace. American Edition, 1892. Online Edition Copyright © 2005 by K. Knight).
The Septuagint has been under revision for two thousand years. Everyone and their brother has been engaged in the revision of the Septuagint. So who is to say that at some point in time, some of the passages of the NT were not placed back into the Septuagint from the NT --- by the likes of Origen for his Hexapla.
I point out that in Origen's day there appeared to be no authoritative Septuagint. He had to use Aquila, Symmachus, and mainly Theodotian to write his fifth column LXX. Why??? What had happened to that beloved Septuagint??? Is it possible that some Christians had been using Aquila and Theodotian, with minor adjustments of course, and then calling them "the Septuagint"???
Origen recognized that there was one Hebrew text and that was in his first column, but he needed four other columns for assistance in writing his LXX in the fifth column. So even Origen recognized that the Hebrew text of his day was unchanging and singular, as did Jerome, but "the Septuagint" was always under perpetual revision and still is today.