I switched off the HTTP proxy cache setting; I was just experimenting anyway. Apparently the entry is still listed even if proxy cache is off. I noticed it also interferes with browsing remote hosts.

Ok, henceforth I will not add IPs to the black list and let the anti-"greedy servent" routines handle leechers.

Otherwise, 3.9.9 seems excellent: loads quickly, searches are fast , and generally seems quite stable. I haven't used any other other P2P packages so I can't really compare, but LimeWire 4 looks like a winner.