Solution : https://service.sap.com/sap/support/notes/813196 (SAP Service marketplace login required)
Key words : 
sales order type -, sales order type, sales information system, terms service contract, billing plan reason, header billing plan, billing plan, quotation type, billing-relevance, system distinguishes
Related Notes : 
       
| 216810 | SIS update with contracts is incorrect | 
| 133939 | SIS: No update for contracts |