Ok, I get your point. However, as I understand it, this is not about restricting the exports of Polish companies, but rather restricting the import of certain goods. Everything depends on how products are handled in every single state, and they can do this pretty independently. So if one country prohibits the import, it doesn't matter where the shipment comes from (inside EU or overseas), and it is also irrelevant whether this product is legal in the country of origin. I don't know of any exceptions. Again, I might be wrong here, so if someone knows a bit more, please share.
Unforunately, there is no uniform, consistent law which applies to all member states of the EU. A ruling on kava in the EU commission should come in a few years, but it doesn't look very good. In general, countries have been restricting and prohibiting our beloved root even more in the past few years -- even without any proper scientific evidence. It's crazy, it's unfair, it's outrageous, but that's how it is.