User blog comment:Necromoni/Probe, The Laser Sentry/@comment-145.93.90.25-20121205110654/@comment-5327869-20121212024758

I think its safe to say that a drone that has been placed as a mine is lost and may be replenished, so 3 can be repairing while 3 is placed. I updated the description to say that a max of 3 drones may be placed as mines.