When your mainhand is set to left, the spear points down. This does not happen when you mainhand is set to right with either hand. This only effects when your mainhand is left not when it is in your left hand. Even when its in your right hand when left handed it still points down.

Steps to reproduce

1. Look in 3rd person with a spear charging

2. Change your main hand to left put it in your offhand and look at it

3. ❌ The spears are held differently