This includes Lynx, CERN, Squid, Midnight Commander and possibly others. Testing showed this to not be a problem for the vast majority of clients available for Unix, Windows and Macintosh systems. All problems reported have to do with directory listings, not general data transfers. Mirror would appear to obtain the directory listing and fail on a subsequent download attempt. The software incorrectly handled the sequence of operations, losing synchronization with the FTP conversation.
Lynx appears to hang indefinitely.
Squid appears to hang indefinitely as well, also only in relation to directory listings. Due to the implementation of Squid, however, the problem is not apparent to the end user. Presently, there is no known correction for Squid. The WU-FTPD Development Group believes the number of clients improperly implementing the FTP is insignificant to the general population. By default, the daemon closes the data connection and expects the client to honor that close before proceeding with the conversation on the control channel.