http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/40d6c489-aa3a-2e10-db88-deb9114b6854?overridelayout=true
After adding new fields into FBL*N screen in config, run BALVBUFDEL to clear buffer. this will solve the issue of blank fields . This may not work for existing layouts, in which case 'Restart' SAP system to clear all buffers..
