MRP - Purchase requisition duedate not before existing Purchase Order

Everything is working as it should. From the Phases of MRP:

Phase 5: Reschedule Existing Receipts

In the process of allocating existing anticipated receipts to demands, MRP always suggests moving the dates of existing orders before recommending any new orders to cover the requirements.  Action messages are generated to indicate the planned rescheduling events, by moving the order date in if necessary to meet an earlier demand, or suggesting the order date move out if earlier than required. In the event the existing receipts exceed the demands for the part, MRP suggests additional actions to cancel those unnecessary orders and/or order quantities.

Phase 6: Generate Planned Receipts

After all the existing inventory and anticipated receipts are applied to meet the requirements, only then does MRP plan new order quantities to cover the future demands. MRP planned receipts can take several forms: Make Receipts for manufactured parts, Buy Receipts for purchased parts, and Distribution Order Receipts for multi-site planned parts. Though not typical, with Manufactured/Acquired Split percentages defined for an inventory part, MRP can generate several of these receipt types in response to a single requirement.  These planned receipts are eventually converted into corresponding order proposals later in the process as described below.

So in your first scenario, the MRP Message of ‘Late Order’ is telling you to move the date of Purchase Order -57 to match the new demand from Customer Order -5903. The new Purchase Requisition -348 was thus generated to cover the demand from Customer Order -5902. Now, a decision is required by the Planner. Do you move the Purchase Order as MRP suggests, or do you change the required date on the Purchase Requisition to match the date for Customer Order -5903?

In the second scenario, the same as above is happening except now moving the Purchase Order for (1) will not fully satisfy the demand for (2) from Customer Order -5903 so a new Purchase Requisition Line for (1) was generated on requisition -51.