this is just a guess, I've used ftp in PHP but I've never tried to share the stream, but...
It looks like you're trying to pass a file descriptor ($ftp_stream or whatever) between to connections, ie. to processes.
every new connection has to reopen the ftp stream, I believe, as that file descriptor for the stream in the last connection is no longer valid.
If you want to connection pool ftp streams, you would need an application server I'm guessing. eg. JSP application server like Apache tomcat http://jakarta.apache.org/
. An application server lets you easily keep variables in "application scope", so that multiple instances ( connection ) can access pooled resources.