3138783 - Manually entered purchase order text disappears with changing certain field(s), why?

If we have a purchase order, into which we entered manually item text, why it disappears with changing plant for example?

And similarly to this, why can manually entered header text disappear?

• Materials Management (MM)
• SAP ERP
• SAP enhancement package for SAP ERP, version for SAP HANA
• SAP enhancement package for SAP ERP
• SAP S/4HANA

text item long header langtext me21n me22n me23n BAPI_PO_CREATE1 manual manually change änderung, Create Purchase order advanced APP , KBA , MM-PUR-GF-TEXT , Texts , MM-PUR-PO , Purchase Orders , MM-PUR-PO-GUI , Userinterface - Purchase Orders , MM-PUR-PO-BAPI , BAPIs - Purchase order , MM-FIO-PUR-PO , Fiori UI for Purchase Orders , Problem