Solution : https://service.sap.com/sap/support/notes/1133183 (SAP Service marketplace login required)
Key words :
st05/st12 performance trace shows multiple inserts, 489 coep execstm 12 insert values, 755 coep execstm 12 insert values, 665 coep execstm 12 insert values, 067 coep execstm 12 insert values, 979 coep execstm 12 insert values, 606 coep execstm 12 insert values, 558 coep execstm 12 insert values, 039 coep execstm 12 insert values, 047 coep execstm 12 insert values