wu-ftpd-2.4.2b18-2.1 has been built with case sensitive commands. Ftp clients sending uppercase commands fail. ftp> GET testfile ?Invalid command
I have verified that upper case commands do not work with the version of wu-ftpd that ships with 5.2.
This is an ftp client rather than a wu-ftpd server problem.
The added functionality of permitting case-insensitive commands is not worth the coist of implementing and testing at this time.