You misunderstood my question, but anyway I found the solution. My problem was that the URL to the post was identical as the URL to the sub-page on the site. So when clicking on the post content the subpage content appeared. Now I changed the URL of the post and it worls well.
Thanks anyway
agrounia.pl, article “Integrowana ochrona roślin od 1 stycznia 2014”
site “Integrowana ochrona roślin”