How are bitcoin trade profits taxed in Poland?
Although I am no polish or live in Poland, I would recommend to claim it as you would do for a investment. If the government finds out your not paying tax, the consequences are far greater than the tax you would pay.

If your not sure then just call the tax department of the Polish government.
On Forbes Cameron Keng has written this  article, check it out and see if it answers your question. I've red it and it does give me a vague answer. 

Hope this has helped