Well, like the Dead Sea Scrolls (DSS), there is evidence that Jewish canon was not uniform. The same is true of the New Testament.
There are significant differences between the Hebrew version (MT) and the Greek version (LXX), as well as DSS.
+Paul was a Pharisee and he probably didn't even see LXX until he started to preach to the Greek-speaking Jews and later on to the Greeks themselves. But, then +Paul is an enigmatic figure and a subject of much debate and even hate and discontent on this thread, so will leave it at that.
Fact remains that the LXX is the backbone of the NT. If it's good enough for the Apostles, it's good enough for the Apostolic Church.
Actually, according to Josephus it was pretty well settled at 22 books (combining certain books, such as the Twelve Minor Prophets, together as single volumes) by the first century (Against Apion, 1.8), which would leave out the Apocrypha. This is substantiated not only from the Apostolic Scriptures (the NT), which never cite the Apocrypha as Scripture, but also from the witness of Philo, Ben Sira, the authors of the Maccabees, Hillel, and Shemmai, which also never cite the Apocrypha as Scripture!
The DSS can't be used to establish normative canon, since in addition to a number of apocryphal works which no current body of the Ekklesia accepts as canon (e.g., the Book of Enoch), they also contain personal letters, practices and standards of the Qumram group, and non-canonical commentaries on the Scriptures. It'd be like finding a Bible with a copy of Irenaeus' Against Heresies, Josephus' Antiquities of the Jews, and the "Gospel" of Peter and assuming that just because they were found with the acknowledged Scriptures that those who collected them believed the latter three to be canon as well!
The same problem occurs when trying to cite collections of the LXX from the fourth or fifth century as establishing the normative canon of the Tanakh from the first.
If it's good enough for the Apostles, it's good enough for the Apostolic Church.
But then, that's the point: It wasn't always good enough for the Apostles. If they saw fit to go back and render a fresh translation from the original Hebrew text in many cases rather than simply citing the LXX consistently, then we should follow their example and do the same.