I've just started using the commons net FTPClient in the past two days and today experienced this same problem with files that have a Feb 29 timestamp. Everything has pointed to a leap-year problem with commons.net.ftp.FTPClient.
All other FTP clients have no problems on the same server (not controlled by me but used by '00s of others).
At least it won't bother us again for another 4 years
Dave