Based on https://forums.factorio.com/109422 not a bug.

Thanks for the reference. This is a bit different as I'm not expecting a different blueprint string format, just additional logging. Everything here is vanilla. A simple "blueprint imported with warnings" message would suffice.

Maybe this ...

1. What did you do?
- Setup elements as specified in the blueprint string below.
- Imported the string into the game.
- Game reports "Blueprint imported successfully."
2. What happened?
- Configuration is imported with a missing connection.
3. What did you expect to happen instead?
- An error is ...

1. What did you do?
- Setup decider combinator as pictured below (A).
2. What happened?
- Combinator outputs a single ("signal-0": 1) as pictured (A).
3. What did you expect to happen instead?
- I expected an additional output of ("signal-1": 2) to also appear on the output.
4. Does it happen ...