Solution : https://service.sap.com/sap/support/notes/485671 (SAP Service marketplace login required)
Key words : 
transaction mc94/mc95, standard sap system, modified source code, modified  perform trunc_changed_details_sop, h485671  perform trunc_changed_details, rounding errors occur, changed rounding logic, rough-cut planning, upper hierarchy level, source code corrections
Related Notes : 
       
| 366256 | Incorrectly rounded values in period split | 
| 126247 | Rounding error in level-by-level planning |