How do I set up an AI mining ship?

I am trying to set up an AI miner. But unfortunately it does not mine any ore.

• I bought a TS class vessel (Demeter). I bought it from an AI pilot and it was explicitly advertised to me as a "miner".
• I equipped it with:
  • 3 x 25MJ shield
  • Mobile Drilling System in the back turret
  • Mineral Scanner
  • Special Command Software
  • Trade Command Software
  • Ore Collector
• Its cargo bay is almost empty (131/3687 units)
• I ordered it to a sector with lots of surveyed asteroids with ore yield between 4 and 41 ("Pontifex' Seclusion" if you want to know exactly)
• I also ordered an M3 Cutlass to "Protect" it just in case.
• I gave it the command "Special..." -> "Mine Minerals..." with these options:
  • "Mineral": "Ore"
  • "Sector": The sector it's already in
  • "Amount": Just mashed numbers, the UI reduced it to "444"
  • "Unload": An AI-controlled station in the same sector which buys ore and has very little left (31 units). The station owners (Paranid) like me enough to let me dock and trade at that station.
  • Click on ">>Mine Minerals"

What the vessel does next is fly a few 100 meter forward and then it reports that it "finished its job" without having mined a single gram of ore. This behavior occurs no matter if I am currently in the same sector or not.

What am I doing wrong?