Certainly something to look further into.
Sure you look. Kupraszewicz as surname seams that isn`t originally Polish. And only God knows how many Serbians finished in Poland after Ottoman Turkish invasion.
Bottom line is that you have Serbians deep in your family tree. If this could be the case, it maybe wasn`t somebody who had surname Kupresanin (Serbian from Lika, Slavonija, Banija, Kordun, Slavonija, Dalmacija, Bosnija or Hercegovina). No, it was maybe just regular Serbian cavalrymen whose origin was exactly from town of Kupres (Bosnia, Hercegovina). Furthermore, I can tell you that if it was originally Serbian Kupresanin chance is 99% that he was Orthodox (after all 99% of legendary Racowie in Poland were Orthodox Serbs- not that there was not Catholic Serbs at that time- it was /at least 50% of all Serbs/ but, it just happened that winged cavalry doctrine was preserved from time immemorial, from deepest Sarmatian past, in regions that were under jurisdiction of Eastern Roman Empire), while if he was some Serbian from Kupres (and he later in Poland on the base of that got Kupraszewicz surname- what was alright to him knowing for logic of Kupresanin surname), chance is I would say 60% that he was Catholic Serbian and 40% that he was Orthodox Serbian. Still, I sincerely believe that it was the case where one Kupresanin served as Racow (forming Winged Cavalry and Husaria) in Poland, later stayed there to live and he or his descendants got change of surname into more Polish sounding - Kupraszewicz. Yes, it must be the case. See, I am more and more sure in it.
Listen what to do if you were to investigate. Considering surname, it shouldn`t be a big problem. If you are Catholic, just go to Church and see for oldest traces of your ancestors who are enlist in Church`s books. You must found first with surname Kupraszewicz. Your first Catholic ancestor in Church books is that original Kupresanin or his son.
Listen this also. If your family had negative issues with Russians, don`t be upset with possibility that somebody who was Orthodox stays in your family tree. See, Serbian Orthodoxy differ from Russian. Actually, our Christianity differ from Christianity of all Slavs. We Serbians within Orthodoxy kept elements of pre-Christian Slavic faith and we still celebrate SLAVA- once universal Slavic family custom. Not to mention that Orthodox Serbians- Racowie in Poland didn`t ask who one was (Catholic or Orthodox) if one acted against Poland, being him German, Russian, anybody. My dear, that how Serbians butchered for Poland, even Poles didn`t butcher. That was loyalty and dedication. There comes the legend about Racowie. After all, there was Sarmatism.
Is.