Why is the po_requisition_update_pub not allowing you to update the attribute_category column for re

I am trying to run the po_requisition_update_pub API to update several requisition lines after the ReqImport has run. The API allows me to update the attribute columns on requisition lines, headers and distributions but not the attribute_category on the lines. I can update the attribute_category on the header and the distributions lines. We have context sensitive DFF on the requisition line and need to update this column with the context value.  Was this an oversight in the code? Below is the error message I am getting.

  L_REQ_LINE_TBL.ATTRIBUTE_CATEGORY := REQ_LINE_REC.LINE_TYPE_ID;