I'm not sure. You might find that they do use supplies, but that they just don't stop working when you run out. Perhaps more of a "feature" than a bug
Are you finding the remote minig economical? Most people find that by the time you've paid maintenence on the mining ship, it's hard to generate a worthwhile amount of resources. A good trick is to find an empty planet with a few moons and send your miner there. It will mine every uncolonised planet, moon and asteroid field in that sector at once, which can double (triple, quadruple) the miner's output.
Or are you playing Devnullmod or something, which has modded various parts of the game to make the remote miners more worthwhile?