In fact it looks like the Storeton pedigree in Ormerod differs from Burke, and asserts that Philip married 1) daughter of Sir Robert Pulford, mother of Joan Stanley and 2) Letitia de Venables (as her 2nd husband), placing Agnes de Storeton as wife of his father, Sir Thomas Bamville.
http://archive.org/stream/historyofcountyp02orme#page/250/mode/1up