Well, not sure this applies to anyone in the world except me, but it sure lead a bunch of ftp gurus on a wild-goose chase until by brute force I discovered the problem’s solution:
the problem: some, but not all, ftp clients (including Apple’s own finder built-in !!!) failed to connect to ftp sites. The key: Apple’s core services was used instead of some unix library.
The solution: Automatic Proxy Discovery was turned on in the advanced tab of Networking prefs.
Turning it off allowed standard FTP to work properly… and had the (subjective) added benefit of speeding up my browser.
Yet Another Trivial Annoyance solved…