River Raid chest keys?

[Dedmoin]

What are those chests keys for?
I don't need them for opening chests and I already have dozens of them.
Probably to unlock the doors from inside? But why I want to do this when I can break the door from the outside anyways?

[Psyringe]

There are specific chests in river raids that require those keys to open. It's easy to overlook those chests because the look like normal small chests and as far as I remember, as long as you have a key, the game just opens them as if they weren't locked (you might get a notification popup for losing the key, not sure). You may have opened several of them already without noticing.