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Well, the question went a week. I did some additional research and I'm offering a plausible response, maybe.
From the Catholic Study Bible, 1 Corinthians was written by Paul in 55 or 56 A.D. Early Christian practices, particularly Communion, weren't codified until the early second century [Wikipedia]. Paul speaks of "the breaking of the bread" as the main part of the Eucharist. It seemed like this caused a point of contention among the early Jewish converts. Afterwards, Paul converted mostly Gentiles [Wikipedia].
However, there was a phase where most catecheses were within synagogues. Peter called the Jersulam Jews of Jesus's time a "crooked generation" [Acts] but the Apostles didn't seem to be ashamed of their Jewish-ness, and their early actions could be seen as reform movements with the Jewish religion--the coming of the Messiah or Massiach--where man and God would once again walk together [Psalm 91].
The Pharisees knew the Mosaic Law, to be sure, but in order to really impress catechesis, they had to use the existing Pentateuch (Torah). In order to do this, they had to find deeper, metaphorical meaning within the Law. Much of this work would have been completed with the Babylonian Talmud (sort of the equivalent of the Catechism) [Wikipedia]. The Pharisees became quite proficient and comfortable with the use of metaphor, especially in spiritual matters.
Perhaps Paul was communicating in such a way. Perhaps he was speaking of the "breaking of the bread" ceremony in which early Christians communed with Christ. I suppose he wished forthe equivalent of taking a blessing or staying in one's seat during modern Communion for those with mortal sin on their soul.
Thus, Paul wasn't literally meaning to avoid one's neighbor, but he was speaking metaphorically to disallow a Eucharistic ceremony for the sinners until ... when, we're not really told when.
Granted, this is an opinion-based answer, but I learned a lot of neat stuff in the process!