Solution : https://service.sap.com/sap/support/notes/93570 (SAP Service marketplace login required)
Key words : 
system activitiesa normal reservation, inserted dummy item, additional key words, material system restrictions, create message co779, insert dependent components, fields resb-bauwg, create phantom components, delete phantom components, delete phantom
Related Notes : 
       
| 101281 | CA01: Upgrade problem for component allocation | 
| 89824 | Field RESB-BAUGR not filled for phantom | 
| 69654 | Phantom assembly with negative quantity | 
| 69107 | Overwriting material -> Component becomes dummy | 
| 66866 | BOM explosion of phantom assemblies | 
| 65429 | Phantom assembly is effective for issue | 
| 64315 | Incorrect level / path for phantom assemblies | 
| 64271 | Prod.order: Field RESB-BAUGR filled incorrectly | 
| 49476 | Costing indicator in dummy | 
| 49376 | Production order: Creating assemblies w. SOBSL '52' |