Solution : https://service.sap.com/sap/support/notes/520748 (SAP Service marketplace login required)
Key words : 
open delivery quantity / open quantity, open quantity key figure, open delivery key figure, open delivery quantity / open, open order quantity, open delivery quantity, gi-posted quantity, open sales order, additional key figures, added key figures
Related Notes : 
       
| 530448 | LIS: Consulting notes | 
| 203266 | SIS setup:Val.fields in deliv., MCLIPS-AP* fields | 
| 125763 | SIS: Collective note - component supplier | 
| 94457 | SIS: "Error determining local currency:..." drng. setup | 
| 69487 | VIS: Updating open order quantity for goods issue | 
| 34232 | MCLIPS-AP*** and MCVBRP-AP*** fields not filled |