In 1883 János Csontosi, the excellent librarian and expert on medieval Hungarian manuscripts published the results of his study tour in Germany. According to his account a summary written by the Franciscan Observant preacher, James of the Marches (1475) on his debate with the rabbi of Buda was preserved in the Bavarian Royal Library in Munich. Since such a work is unknown for the specialists of the subject, the discovery of a text, which provides information on an interesting event in the religious and cultural history of Hungary in the 15th century, would have been expected. However, on the basis of the data (author, copyist of the manuscript) given by Csontosi it proved to be impossible to find traces. Finally, the solution was furnished by the two catalogues printed in the 17th century in the Library of Augsburg, as many of the medieval codices of Munich were transported from there in the beginning of the 19th century. The works of Elias Ehinger and Anton Reiser reveal that the author of the text in reality was Pier Paolo Vergerio the Elder, who made a summary of the debate held in 1433 between James of the Marches and Joseph, rabbi of Buda. The recently published catalogue of the Bavarian State Library confirms these data, but declares that the text in question is missing from the codex (Clm 3590), which contained it formerly. On the other hand, it notifies the fact that the codex was in the possession of John Carpentarius, the Carmelite provincial who stayed often in Buda at the end of the 15th century. Consequently we failed to discover a work of Vergerio, but we have gained precious information on the fact that he wrote such a work, on the activity of James of the Marches in Hungary, and on the interest of a leading figure of the Carmelite order of the age.