Due to the use of the '@' in the FTP URL to separate the user from the host name. If the users password has an '@' sign, the URL has 2 '@' characters and therefore causes problems.
Non-anonymous FTP has been removed from the installer starting with release 6.1, so this is no longer a problem. I am putting the report on a list of things to consider when and if we reimplement non-anonymous FTP installations.
*** Bug 2458 has been marked as a duplicate of this bug. ***