Solution : https://service.sap.com/sap/support/notes/542054 (SAP Service marketplace login required)
Key words :
field but050-dftval start transaction se38 enter, lt_but050 type standard table, field but050-dftval, clear lt_but050-dftval, program 'executable program', long time depending, update but050, numeric field, char field, table lt_but050
Related Notes :
| 398888 | BP_TR1: Composite note and FAQs about bus partner conversion |