According to Marianne Cassirer509
Gertrud Buchhorn, (b. 13 May, 1876-11 January, 1964), wrote that the grandfather of her grandfather, "Bujakow", was a cashier at a "Grafen" (estate of a person of high rank similar to a lord or earl). Bujakow was given the name of Cassirer. Thus the Grandfather of her grandfather was named Bujakow. (He may also have lived in Bukajow, a place in Poland near Rynek and not very far from Katowice.510
It is highly probable that Gertrud's father was Leopold Cassirer, her grandfather was Salomon Cassirer, her great grandfather (father of her grandfather) was Mausche Cassirer, and that the grandfather of her grandfather was thus Loebel Moses Cassirer.
This would mean that as was common at the time, Loebel Moses ben Jakob took the family name “Cassirer” from his occupation as cashier.