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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