3625025 - Default units of measure in purchase requisitions and purchase orders

In master data it is possible to define a base unit of measure and an ordering unit of measure (variable Order Unit).
When a variable order unit is set in the material master and/or purchasing info record master data it not clear how the system determines the default Unit of Measure when creating purchase requisitions and purchase orders 

SAP S/4HANA Cloud Public Edition

1. Create a Purchase requisition using APP 'create purchase requisition advanced' (ME51n) or one of the procurement fiori apps
2. Create a Purchase order with reference to the purchase requisition using APP 'create purchase order advanced' (ME21n) or one of the procurement fiori apps

standard system behaviour

1 - In a purchase requisition the base unit of measure is ALWAYS adopted automatically from the material master record
2 - The default order unit in the purchase order is assigned according to the following priority: 

• reference purchase order
• reference contract 
• reference purchase requisition (if the variable unit is active in the material) 
• Purchasing info record 
• reference purchase requisition (if the variable unit is NOT active in the material)
  .... other combinations including without a material ID follow 

alternative unit of measure, purchase requisition, default unit, material master, purchasing tab, variable order unit, source of supply tab, 06147, LMEPOF6D, MEPO_ITEM_FILL_MEINS, eban-bmein, eina-meins, eban-meins, mt06e-bstme,
mt06e-vabme,  eina-vabme,  ME_PROOF_VARIABLE_ORDERUNIT   , KBA , MM-PUR-PO-2CL , Purchase Orders (Public Cloud) , MM-PUR-REQ-2CL , Purchase Requisitions (Public Cloud) , MM-FIO-PUR-PO-2CL , Fiori UI for Purchase Orders (Public Cloud) , MM-PUR-REQ-SSP-2CL , Fiori UI for Self Service Procurement (Public Cloud) , Problem