I also think the relation is missing in BOL Model. Check transaction GENIL_MODEL_BROWSER for HRPAD object. See if the relation is there for IT0019_REL. If not you can edit using report HRPAD_R_EDIT_MODEL.
See the below link for details -
http://help.sap.com/erp2005_ehp_05/helpdata/en/d2/595bb22efd4a748a31c391efa0ee88/content.htm