P: Synchronize folder creates duplicates when non-Latin letters are used

I have a problem - with folders containing Polish letters... I did "synchronize" on main folder, as I copied a bunch of folders with pictures from another disc into, and suddenly pictures I had in the catalog for years showed up again. And if I look into the library, the same picture is displayed, say, 5 times. If I select four of the thumbnails and tell Lightroom to remove the pictures from the catalog, all 5 are gone (even the one I haven't selected) - so it is not a problem of duplicated files, but a corrupted catalog. Of course I've checked the folder in Explorer and the files are not duplicated. Seems that Lightroom has a problem with non-Latin characters... Other users report the same issue with German, Greek etc.