Solution : https://service.sap.com/sap/support/notes/390620 (SAP Service marketplace login required)
Key words : 
directly superior wbs component, automatic total calculation, manual planning reason, cost element planning, wbs element, structure planning, planning profile, planning transactions, automatically totalled, terms cj40
Related Notes : 
       
| 1235375 | PS reporting: Plan for higher-level WBS elements too low | 
| 584655 | Automatic total up without structure plan values | 
| 535158 | CJ40, CJ42: Total up function | 
| 382379 | Cost Element Dependent planning in the PS hierarchy report |