Spell-casting items using mana

[Drawde]

I don't know if this is fixable, but something I noticed today when testing is that items that cast spells (wands, potions etc) actually use up your mana, as if you had cast the spell yourself. They don't check your mana when you use them, so you can end up with negative mana this way!
Also, "charged" items like potions have infinite charges, but I assume you already know this.