Mekanism version: 1.7.10-8.0.2.201

If you fire the flamethrower across the floor, 1/10 of the flame sprites will not "despawn" when the actual fire object (which hurts you) extinguishes.

Firing a flamethrower trail on the floor:

After 10 seconds, there are still some fire sprites left behind, they don't burn. They will go away if you reload the game:

By flame sprites, do you mean the flame "blocks" that are in the snow?
Edit:
I was setting the block to fire on the client which was causing the issue. Fixed in development.

By flame sprites, do you mean the flame "blocks" that are in the snow?

Yes, flame blocks. I wasn't sure those are also blocks or tile entities or something else.