Another way around the problem is to have damage done to the contents when the container via magic. The assumption is that the violence of the fireball/etc. damaged one or more items, damaging or destroying them. I've played several other games that handled it that way. Then you have the choice of lock-picking (if you've got the skill), bashing with a weapon (and the weapon takes damage), or using a combat spell (and the items you're trying to get might be damaged or destroyed).
Yeah, that suggestion has popped up before, but the problem is that while it makes sense on chests, it doesn't make sense for locked doors that lead to profitable areas. It's hard to justify damaging the contents of a room for a locked door that was blasted with spells down the hall, around the corner and beyond another door at the base of a set of stairs.
I'm honestly ready for locked doors/containers to be immune to magic damage.
