PO Approval notifications not routed correctly

Hello,
PO approval notifications are not being routed correctly.
In our DEV instance, we have setup the profile options as below to route all Procurement notifications to a mailbox.

• PO_CONTROL_SUPPLIER_COMMUNICATION: Override E-mail Recipient
• PO_NOTIFICATION_OVERRIDE_E-MAIL: UATGSICKH@three.com
  

This correctly routes both PO approval notifications and PO print to supplier address to the mailbox UATGSICKH@three.com.
Then, we change the profile options as per below:

• PO_CONTROL_SUPPLIER_COMMUNICATION: Enable
• PO_NOTIFICATION_OVERRIDE_E-MAIL: null (empty)
  After doing this, only PO print to supplier address is routed to the email we specify in PO header, but the PO approval notifications are still being routed to the mailbox UATGSICKH@three.com, which is incorrect.