Odd results in SELECT

Can anyone suggest why this might be happening (I think it's in 7.1b4):

SELECT definition as viewdef,
(select oid from pg_rewrite where
rulename='_RETszallitolevel_tetele_ervenyes') as view_oid
from pg_views where viewname = 'szallitolevel_tetele_ervenyes';

=> view_oid is 133652.

SELECT definition as viewdef,
(select oid from pg_rewrite where
rulename='_RET' || 'szallitolevel_tetele_ervenyes') as view_oid
from pg_views where viewname = 'szallitolevel_tetele_ervenyes';

=> view_oid is NULL

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