Great catch! Yes, SENSE TEST is intentionally a very strong assist feature. If you run it against 00000000, it can indeed reveal the hidden bit pattern row by row: correct zeroes stay zero, wrong zeroes point to ones. So this is not really a bug, but more like a “guided / educational” way to solve the game.
For the purer challenge, players should use only TEST ROW, with CORE MATCH and VALUE TOO LOW / TOO HIGH clues. SENSE TEST is there for learning, experimenting, or when you get stuck.
I may add a harder mode later where SENSE TEST is limited, penalized, or disabled.
Thank You! :)