I encountered a bug that persists in 1.6.1 even after hard reset.
My first skillmine option after unlocking skillmine doesnt finish properly, after all fields are mined out, I dont get a choice of three options as I should, instead skillmine shows the one with all fields mined out and assigned workers finish some virtual field (same bonus as the last real field they worked on) at rapid speed (the bonus gets increased several times per second with only 14 workers).
Also, there should be some limits to certain benefits from skillmine. While some of the bonuses can be stacked unlimitedly (I assume more pixels, more damage, extra idle hitters), some should be limited to avoid chance of them making game unplayable (faster idle hitters bonus should never exceed -5s, perhaps limit should be -4.5s?). The other bonuses (chance for clicks to hit twice, chance for idle hits to chain, cheaper upgrades, instakill chance) should or shouldnt be limited to 100 percent, that depends on how they work.