Does the API for cancelling POs work in encumbrance accounting

We are calling the API apps.po_document_control_pub.control_document to cancel open encumbered POs, and receiving the error message "Your Budgetary Control action completed with exceptions."

We are able to cancel the same POs from forms, we are not enforcing any budgetary control rules, the code combinations are valid and enabled, and the PO and GL periods are open.

Should the API be able to work with encumbered POs?

Andy