Solution : https://service.sap.com/sap/support/notes/513781 (SAP Service marketplace login required)
Key words : 
terms manual product selection, manual product selection, item texts reason, product selection, item texts, dialog box, alternative material, entered material, system determines, text determination
Related Notes : 
       
| 509918 | Changing the order type: No item category available | 
| 482346 | Incorrect text determination with set cross selling | 
| 458385 | SD document: creation w/ reference -> error in text dtrmntn | 
| 318538 | Error in text determinatn with manual prod.selectn |