Postgres data changes visibility rule: during a query execution, data changes made by the query itself (via SQL-function, SPI-function, triggers) are invisible to the query scan. For example, in query INSERT INTO a SELECT * FROM a tuples inserted are invisible for SELECT's scan. In effect, this duplicates the database table within itself (subject to unique index rules, of course) without recursing.
Changes made by query Q are visible to queries that are started after query Q, no matter whether they are started inside Q (during the execution of Q) or after Q is done.
Read the upstream documentation. For corrections, first check the current version.