Solution : https://service.sap.com/sap/support/notes/517897 (SAP Service marketplace login required)
Key words : 
long runtimes occur, error behaviour occurs, sales orders, back update, backorder processing, running simultaneously, terms transactions, /sapapo/bop, /sapapo/bopi, /sapapo/bop_update
Related Notes : 
       
| 609435 | Composite SAP note: Performance in backorder processing | 
| 512646 | Temporary quantity assignments are not cleared | 
| 420598 | Composite SAP Note for GATP performance in APO 3.1 | 
| 375193 | Backorder processing: Composite SAP note on posting |