Firefly bushes aren't randomly offset, unlike similar blocks

Firefly bushes don't have the random offset when placed, unlike similar blocks such as grass or flowers.

How to reproduce

1. Place around 8 firefly bushes along a line of grass blocks.
2. Place around 8 short grass along another line of grass blocks.
3. Notice the difference in placement.

Expected result
Firefly bushes would be randomly offset, similar to other foliage.

Observed result
Firefly bushes are fixed to the center.