This problem was fixed in version 1.5.1 (released 1 May, 2007), but you can avoid it in your version simply by setting the DISABLE_CHMOD_AFTER_PUT flag in SSHFTPClient. You do this as follows:
sftpClient.setConfigFlags(SSLFTPClient.ConfigFlags.DISABLE_CHMOD_AFTER_PUT);
If you are able to upgrade to the latest version then that would be advisable of course.