Hi raff,
Receiving a PO using the mobile app results in the PO Line becoming Registered, but the PO itself does not automatically become 'Received'. As you say, it is possible to receive a PO on the mobile app even if the PO has the Status = Approved (i.e. it is not Confirmed).
This mirrors behaviour that you get if you are not using the Warehouse module. i.e., it is possible to use Inventory Registration on a PO which is not Confirmed.
Note that in all cases, it is not possible to post the Product receipt (GRN) for a PO which is not Confirmed.
I noticed a fairly recent hotfix for R3: KB 4026019: Inbound work creation when PO is not confirmed. The description is: The changes in the hotfix make sure: When you do purchase receive via mobile device, if the current purchase is not approved or confirmed, throw an error message to block from proceeding.
So I think the design is clear; unless the PO is still in workflow (Draft, In review), it should be possible to receive the PO on a HHT.
In real-life, it allows the inventory in F&O to reflect reality. If the Vendor has delivered PO123, even if PO123 is not Confirmed, it allows F&O to show that the items have arrived.
Are you sure that it allows PO Workflow to be bypassed? The mobile app should not allow you to receive a PO which is not Approved.