Can't use rockets as propellers

^{Description updated by [Mojang] Mega_Spud (Jay Wells)}
Verification builds:
1.2.0.2 Retail

Summary:
Firework rockets don't provide elytra boost if you are gliding close to the ground.

Steps to Reproduce:

1. Jump off a block <5 blocks above the ground
2. Immediately activate elytra to begin gliding
3. Try and use a firework rocket to propel yourself forwards

Observed Results:
The firework rocket will not activate at all, unless you are ~10 blocks + above the ground

Expected Results:
You should be able to use firework rockets at any height, if you are actively gliding with elytra

Screenshots/Videos attached: Yes

Notes:

Original Description:
Fireworks cannot be used as propellers in elytra like on Java Edition