Approval Routing for Purchase Orders for *OPxx Items

I am unable to get Approval Routings to work with PO's for Outside Process Items (*OPxx).  The R31410 generates the PO using a version of P4310 that specifies use of the approval route in the B/P Constants.  Even though the PO is generated with the correct statuses for approvals, the PO does not appear in the P43081 screen.  I also tried by specifying the route in the P4310 processing options with no success.  Any idea what I may have missed in the setup, or do outside processing items never go through approval routings?  Any help will be greatly appreciated.