Cancelling PO @ Header Involing Std PO Approval WF though Doc Type Points to Custom PO Approval WF

All,

We are on R12.1.3.

As part of the solution PO Approval Workflow has been customized and we have created a custom copy of it.

Purchasing Document Types has been updated to reflect the custom PO Approval WF.

The process works fine for PO approval for Std PO.

But when we cancel a Std PO and enabled the E-Mail check-box to send a notification to a specific email address, it invokes the standard PO Approval Workflow.

Any idea how this be changed to invoke the custom PO Approval which has the call the custom PO print process?

We use only Std PO.