Emissive blocks don't emit light when held

When holding emissive items (torches, glowstone, sea lanterns, or custom blocks with an emissive map,) these don't emit any light.

Steps to Reproduce:

1. Hold emissive item in either mainhand or offhand slot

Observed Results:

Item loses all emissive properties

Expected Results:

Item emits light as if the block was placed down at the position of the player.