Hello.
If you try to Pick Up a Coracle in Deep Water, you have two scenarios:
1. If your cape slot is empty, the coracle will be instantly picked up in this slot.
You are now swimming in deep water, and you can't drop the coracle back, because you can't click to pick up items from your inventory or equipory or directly drop them (ctrl+click) while swimming.
2. If your cape slot is not empty, the coracle will be picked up and held on your cursor.
You are now swimming in deep water, with a coracle on your cursor. You can only drop it back in the water, since you can't place it from your cursor into your inventory or swap it in the equipory while swimming.
Here's a video showing both scenarios, in your vanilla client: https://youtu.be/VJrJzUX0zY0
Scenario #1 doesn't seem like the intended behavior to me. We shouldn't be drowning with a coracle on our back.
EDIT: So to clarify, you should NOT be able to put it on your back while you're in deep water either.
Thanks.