The bug

When you cast a fishing rod and swap items with another fishing rod the player is still fishing.

Other items might be affected as well.

How to reproduce

1. Place an unused fishing rod in your mainhand and your offhand
2. Select the fishing rod in your mainhand and cast it
3. Press F to swap the items
4. Stop fishing

You will see that the fishing rod which was at the beginning in your offhand (which is now in your mainhand) gets damaged