It happens on my characters. Even they are on rest mode they can still mine. The problem is i cannot use any potions on them. Only available item is another shift. 

Yes you might think they are on cooldown, but theres no cooldown timer. I can simply use another shift item to normally use them. But why they can mine even on sleep mode? 

PS. I used the extra shift and it shows cd. But can still mine even on rest mode.