Summary: When your holding a fishing rod in third-person, your main hand doesn't move like the off-hand does. It only affects fishing rods, not anything else (even the Carrot/Warped Fungus on a stick isn't affected)

Steps to reproduce:

1. Give yourself a fishing rod (doesn't have to be enchanted)
2. (Optional) Turn "View Bobbing" Off (this helps make it more noticeable)
3. Go into third-person mode and start walking in a flat area

Observed Result: The main-hand doesn't move

Expected Result: The main-hand should be moving

Video: Yes (sorry if it's too fuzzy or blurry to see the bug, I retried the video many times but I can't do anything about it.)