Version:            (using KDE 3.5.9)
Installed from:    SuSE RPMs
OS:                Linux

Sorry, bug 127793 is not fixed for all ftp servers. I am using z/OS 1.8 (IBM mainframe) with default configuration. If I try to rename a file to an existing one the following conversation happens:
Request: SIZE /home/user/x
Response: 501 command aborted -- FTP server not configured for SIZE
Request: cwd /home/user/x
Response: 550 CWD cmd failed : EDC5135I Not a directory. (errno2=0x0519004F)
Request: RNFR x_1
Response: 350 RNFR accepted. Please supply new name for RNTO.
Request: RNTO /home/user/x
Response: 250 /home/user/x_1 renamed to /home/user/x 


I changed the source of ftp.cc/ftp.cpp to fix this:

bool Ftp::ftpFileExists(const QString& path)
{
  QCString buf;
  buf = "RNFR ";
  buf += remoteEncoding()->encode(path);
  if( !ftpSendCmd( buf ) || (m_iRespCode != 350) )
  return false;

  // skip leading "550 " (response code)
  const char* psz = ftpResponse(4);
  return psz != 0;
}