MetaBox - nationalization characters

Why Metabox input field does not save characters nationalities such as the "ęśćó" and so on. Only saves some strange codes "u0107" and so on.
Could you answer how to solve this problem?

Thank you
Paul
(https://cloud.githubusercontent.com/assets/5786280/18160797/4d26802a-702f-11e6-818c-d1faa99bb165.png)
