Coal mine bug when missing settlers

I was lacking settlers, built about 20 wells, then a coal mine (level 2, on a 2900 coals deposit). So I had to wait 4 or 5 hours before it gets its settler in, but after some minutes there was 2892 coals.

I refreshed my browser and re-logged in: coal mine still says "Status: Working" and "Missing: Settlers". It consumes the deposit's coal. I don't know if coal is added to my storehouse (I guess not). I'm stopping it until settlers will be available.

Cheers
Pdor