If I buy a vehicle in another state I then get a transport tag, I use that to get it back to my home state and then register it, it gets titled in the state it is purchased and a temporary registration, then the title is transferred to the residence state.
In Poland is there a title process. What if you have a lien on a vehicle how is that recorded, here you only get the title when you own it outright, as in paid cash, if you borrowed to buy it then you get a memorandum title until the loan is paid in full.
Does Poland offer temporary registrations for transporting to another EU state, If I buy a EVO 300 Junak in Poland it has to conform to all EU standards. I do not live in Poland I do not need to register it there I do not have residency there. I only need registration to ride it and it gets registered later in another EU state that I have residency in.
The same would be true for the Ukraine, if the model sold in the Ukraine was an EU conforming model.
What matters is that the vehicle is on the EU list as conforming and that the country of purchase offers temporary registration. If they do not then it has to be shipped and then it is not worth it.

Taxes get paid on registration, I would think.