Watch the closing credits of some of the episodes of "I Love Lucy". In certain episodes Desi's name is spelled wrong. It says "Conducting the Dezi Arnaz Orchestra" or something of that nature. Desi is supposed to be spelled with an S, not a Z! Pretty big mistake for "DesiLu Productions" to make.
It wasn't Desilu that made the mistake. It was CBS. They bought the rights to "I Love Lucy" and created the heart logo we all know and love. (Before, it was animated portrayals of Lucy and Desi.) So, when they were doing the ending credits, CBS messed up and spelled Desi "Dezi".