Solution : https://service.sap.com/sap/support/notes/418336 (SAP Service marketplace login required)
Key words : 
additional key words subitem, maintain subitems manually, set processing scenario, delete items, program error, solution implement, attached corrections, configuration, prerequisites, note 417685
Related Notes : 
       
| 417685 | Sales order (Set): Components in the sales document | 
| 365327 | Incorrect components in sales order for SET processing | 
| 334782 | Configuration - double sub-items II | 
| 329927 | Configuration - duplicated sub-items |