Multishot arrows do not spread when aiming up or down

When firing a crossbow with multishot, the dispersion of the arrows or rockets decreases as the firing angle increases/decreases.

Steps to Reproduce:

• Enchant a crossbow with multishot
• Aim to the sky or to the ground (while fly a few blocks above it). 
• Reload and shoot.

Observed Results:

The arrows (or fireworks) don't spread and follow the same trajectory.

Expected Results:

The arrows spread as if you were aiming horizontally