Strange and very difficult to replicate situation:

>invent
You are holding a shifting alchemy satchel in your right hand and a plain steel key in your left hand.
You are wearing a slender black components kit (lockable).
>unlock kit
You might not want to do that. Manipulating phased items is difficult.
You hear a click as it unlocks.
>lock kit
You might not want to do that. Manipulating phased items is difficult.
You hear a click as it locks.

Only happens when holding a PHASED object/container in the RIGHT hand, and unlocking another item.

You can phase containers whether or not the container is lockable. Phasing an unlocked contained does not affect the weight of the contents. I think it's not a bug. Supposed you find a container while hunting. It might weigh nine pounds, but you can phase it, even though you can't lock it, to reduce encumbrance while you continue your hunt.