Solution : https://service.sap.com/sap/support/notes/446833 (SAP Service marketplace login required)
Key words : 
import relevant subcontracting purchase order, import relevant subcontracting items, control break instruction, subcontracting items, terms subcontracting, control break, symptom problem, seldom cases, wrong price, scheduling lines
Related Notes : 
       
| 747665 | Calculation of GWLB condition, while posting GR for Sch.Agr | 
| 531754 | Import relevant SC order, GWLB not calculated correctly | 
| 397846 | Import relevant SC order, GWLB not determined |