Not necessarily a bug: there may exist two distinct hosts at the same IP, trying to connect to you through the same firewall or NAT routing device...

Why do you think that these hosts are not firewalled or NAT-routed? It's possible, for NAT-routed hosts on the same LAN sharing the same Internet access, to create independant connections to the same target UltraPeer on the Net, and these two hosts on the same LAN way still be able to accept incoming connections on the same port.

These two hosts do not communicate each other to check their mutual connections attempts.

But usually the UltraPeer will disconnect one of them, à priori the most recently connected one that will have to seek for another UltraPeer...

But normally, the first Gnutella packet that a Limewire leaf node sends to an UltraPeer is a connection header specifying on which port they expect to receive incoming connections, as well as their own Gnutella servent GUID and IP address and port number within the first Gnutella message sent which should be a direct PING with TTL=1 and Hops=0 (so that this ping message will not be relayed to other hosts, but will just feed the UltraPeer pong cache, and will setup a routing path for QueryHits to forward after the leaf has relayed a Query through your UltraPeer.)

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