When you have a container in your inventory with the same name as containers on the ground:
Specifying a number with look considers all containers visible.
Specifying a number with get or put considers only containers on the ground.
E.g. with 10 "chests" on ground and 1 in inventory, you may look chest 11 to see the contents of the 10th one on ground, but you will have to get item chest 10 to actually interact with it.