Yeah, I noticed a similar sort of issue… On my vmware internal network for development, running two Syncthing instances, they contact the discovery server over IPv4 and then seem to switch over to IPv6 to talk directly to one another over the virtual switch, based on what I see in the wireshark logs.
I don’t think Syncthing is talking over NAT to the Internet via IPv6 – just doing it internally on the vmware switch.
Probably I’ll need to do the same thing (disable it in the config, or globally in Linux) because I’m not set up for IPv6 either.
Cydron, your thing is something different. I don’t see a problem there. Sounds like they are doing local discovery on v6 and connecting that way - all good?