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 which even Jews of the 1st century BC often criticized as being full of interpolations, paraphrases, and inaccuracies.
The tradition of reading from these often inaccurate and paraphrased Greek texts after reading from the Hebrew was a Pharisaical tradition. It appeared to have been a tradition, which if the translation reflected the Hebrew was no problem, but if not, then it was one of those many traditions of the Pharisees [Mark 7;13], that Jesus criticized as making "the word of God of no effect."
>> 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.