ToME: the Tales of Maj'Eyal

This seems like a bug... but maybe there are some conditions to be met I'm not aware of:

I have found the artifact "Arkenstone of Thrain". Initially it has "150 power" and it takes "100 power" to use. Using it it goes down to 50/150 as expected, but later it never goes up again. I've tried spending turns with the item equoipped and unequipped, neither will do. Maybe this is intentional and you need something to recharge it. In this case, rather than a bug in the behaviour, there would be a "typo" in the message when you try to use it, that says "Arkenstone of Thrain is still recharging", from which you expect it to recharge by itself.