Solution : https://service.sap.com/sap/support/notes/570623 (SAP Service marketplace login required)
Key words : 
terms order bapis reason, statement clear et_return, possibly existing messages, data formatting, final return, return table, solution implement, program correction, bapi_alm_order_maintain, documentation
Related Notes : 
       
| 708508 | Downgrade BAPI_ALM_ORDER_MAINTAIN -> errors |