Upon a closer examination of Gal. 2 and Acts 15, perhaps the redactors didn't miss that one. The council of Jerusalem in Acts is a conflation of two different discussions, distinguished in Gal. 2:1-10 and 2:11-14, one concerning circumcision and the other concerning dietary regulations. Luke combined two distinct controversies and their varying solutions (Paul distinguishes them more clearly in Gal. 2). One controversy was about the obligations fo convert Gentiles to observe the Law, and Peter and Paul both took part, see Gal. 2:1-10; the other controversy which took place later was about the social relations between groups of Christian converts, those from Judaism and those from paganism, see Gal. 2:11-14. In this James, in Peter's absence, took the leading part. Any contact with gentiles involved legal impurity for Jews. See Acts 15:20.
Whatever the case in Gal. 2, it is apparent that Paul is not creating a schism. He is not breaking the link to the mother church at Jerusalem, here represented by the three "recognised leaders," the "pillars" of vs. 9; that is why Paul felt the collection for the "poor" in Jerusalem to be important (vs. 10 and 1 Cor. 16:1).