Solution : https://service.sap.com/sap/support/notes/386029 (SAP Service marketplace login required)
Key words : 
additional key words mir6, carried outan assignment, program error due, /3 support packag sapkh46c13, /3 support package, credit memo, transaction/event, subsequent debit, subsequent credit, item level
Related Notes : 
       
| 373124 | MIRO: Incorrect amounts on GR/IR clearing account | 
| 366865 | MIR6: Change trans. (e.g. invoice to subseq.debit) |