Reference: Advanced FTP Server Options
This option tells the ftp client interface to ignore case when processing directory and file status information. Any request for file information results in the retrieval of a complete directory listing. This listing is then searched locally for the matching file name(s). This can add overhead when a directory contains a large number of files.
Note: Your user account must have rights to directory listings. Case sensitivity is imposed by the FTP server, and can be overcome only by performing name matching in the client. If we cannot retrieve lists of names, we cannot translate case.