select oid .... for update ....

Here's something I don't understand....  If I'm missing an obvious, please
feel free to kick me in the right direction.We're given two tables, linked with a foreign key. When insert is run on a
master table, everything is OK, when  trying to insert into a detail table,
a strange query appears in the log (schema and log snippet attached).In fact, there should  be no problem, but if a
user has no permissions to
 
update the master  table (eg, this is  a log where he can  only insert, but
neither  delete, nor  update), then  inserting into  detail table  fails on
permission violation at the query:

SELECT oid FROM "alpha" WHERE "id" = $1 FOR UPDATE OF "alpha"
TIA
Ed


---Well I tried to be meek And I have tried to be mildBut I spat like a woman And I sulked like a childI have lived
behindthe walls That have made me aloneStriven for peace Which I never have known
 
Dire Straits, Brothers In Arms, The Man's Too Strong (Knopfler)