During proper behavior, the chronology is:

1. INSERT INTO CartLine (child) with positioner=0
2. UPDATE Cart (parent)
3. UPDATE CartLine set positioner=? for each CartLine in Cart, setting positioner from 0 to number of children

During improper behavior, the chronology is:

1. INSERT INTO CartLine (child) with positioner=0
2. UPDATE Cart (parent)
3. UPDATE CartLine set positioner=? for each CartLine in Cart, setting positioner from 0 to number of children
4. UPDATE CartLine for each CartLine in Cart, updating all fields, and re-setting positioner to improper value