
When I demolish the miner and check the squares underneath by hand, two of them show negative values. Mining makes the negative value greater (i.e. -2500 ==> -2501). There are also at least two in the copper field in the north west end of the base in this save (let me know when you've grabbed it so I can pull the link, tia); I can't remember if I've seen this in any other levels or in freeplay. e/ I should clarify, this is level 4 of New Hope.
Probably somewhat related to this one, even if it's not the same code block causing it.