Glad to hear that your grandparents are not Jew-haters but the history of Polish anti-semitism is quite extensive.
Even after WWII, when Jewish survivors attempted to return to their homes, the Polish people had pogroms against them. I have actually visited Poland and there are graffiti swastikas all over the place.
Recently a Polish MP blamed all of Poland problem's on the Jews.
There are around 5 Jews living in Poland currently. It's amazing how they are able to cause so many problems.