The bug

These blocks consist of a thin covering on top of either dirt or netherrack. Their dedicated particles do not seem consistent.

• Grass block: produces dirt particles
• Mycelium: produces mycelium side particles
• Podzol: produces podzol side particles
• Crimson nylium: produces crimson nylium side particles
• Warped nylium: produces warped nylium side particles
• Grass path: produces dirt particles

How to fix

There are multiple ways this could be solved:

• All of these blocks should use dirt/netherrack for their particle textures
• All of these blocks should use their side textures for particles
• Models should be able to define multiple particle textures per block (possibly with weights), and the models would define the bottom, side and top textures as possible particle textures to pick from when creating particles