Now that Belgian guy has a problem because he is trying to open a bank account, and without a KP that is not possible.
I bet you any money that the bank is PKO Bank Polski as they are renown for their inflexibility and stubbornness.
I had a British friend of mine who tried to open a bank account last year and they wanted a working visa from him, which was abolished for EU nationals when Poland joined the EU in 2004.
Tell him to try the Millennium bank as they have a much more modern approach to their customers, and explain the situation to them.