Not sure it helps, but I have a guess as to the reason - it may have to do with UDP checksum and tunneling through IPv6. Basically, UDP checksum is optional in IPv4, but not in IPv6, and a wrong or missing (all zeros) UDP checksum will result in a packet being dropped. What I suspect/guess might be...

So what about blueprinting as signle signal and placing it at illegal positions? I suppose it's possible to work around the limitation that way. My guess is blueprints wouldn't put them in illegal spots, much the same as blueprints don't put mining drills down on illegal spots The indication of pos...