I've done a search on these forums for "Endless Copper Mine" and for "Quality Copper Mineshafts" but cannot see anyone else mentioning this "bug" so here we go...
Copper Mine: production time = 3 mins
Endless Copper Mine: production time = 3 mins
Copper Mine on a Quality Copper Mineshaft: production time = 1 min 30 seconds
Endless Copper Mine on a Quality Copper Mineshaft: production time = 3 mins
Something does not stack up here. I've seen nothing stating that Endless Copper Mines do not benefit from being built on Quality Copper Mineshafts as discovered by geologist with the appropriate skill.
BB can this please be addressed.