Solution : https://service.sap.com/sap/support/notes/771448 (SAP Service marketplace login required)
Key words : 
terms long text reason, enter text, prerequisites text, text change, bapi bapi_alm_order_maintain, 'commit work', subsequently changed, function routines, solution install, order change
Related Notes : 
       
| 809444 | BAPI: No transfer of contract change | 
| 708508 | Downgrade BAPI_ALM_ORDER_MAINTAIN -> errors |