Solution : https://service.sap.com/sap/support/notes/86748 (SAP Service marketplace login required)
Key words : 
additional key words component allocation, attched source code corrections, multi-level basis, fixed bom application, component allocation, bom application, bom selection, bom explosion, bom header, phantom assemblies
Related Notes : 
       
| 142911 | Comp. asnmt phantm assmly incorrect via classes | 
| 138789 | BOM explosion with different usages | 
| 135480 | Explosion of phantom assemblies in order and plan | 
| 82920 | Component allocation of phantom assemblies (BOM) | 
| 73107 | Allocation of phantom assemblies in productn order | 
| 73097 | Not production-related assemblies in the routing |