Isn't the bigger issue that the father forgave the son even though the son was not truly repentant but he only came back because he was hungry?
Kind of blows the "shunning" practice to bits doesn't it? The father should have shunned the son until he was "truly" repentant.
Also bear in mind that the father ran to meet his son. He didn't wait to see how repentant his son was before calling for a feast!