The Bug
When bonemealing rooted dirt when it is adjacent to other blocks of rooted dirt it creates more particles then it does when not next to other rooted dirt
Reproduce
Place one piece of rooted dirt
Bone meal it
Notice how only a few particles are made
Place more rooted dirt around it
Notice more particles than before
Plausible Reasoning
I'd assume the game is attempting to make more hanging roots on the adjacent Rooted Dirt blocks but only one is being made thus causing more particles
Can confirm.