Strange row locking - question

Hi all,

When I update row in table with foring key, referenced row is locked. I
can see it in log file:

DEBUG:  query: update entry set sometext = 'aaa' where id = 1;
DEBUG:  query: SELECT 1 FROM ONLY "languages" WHERE "id" = $1 FOR UPDATE
OF "languages"

When I execute update second time I receive only this:

query: update entry set sometext = 'aaa' where id = 1;

Referenced row is locked only first time ? This behavior looks me little
bit strange. Can anybody explain it ?

Regards,

Vaclav