Update: OVERKILL fixed this in the latest update. This mod is now pointless. Way to go, them!

To put it very simply: The clbk_impact and on_collision functions can run several times in a row when the grenade actually collides in a single frame as the engine tends to handle that stuff and is not very precise about it.

Since the game never accounts for this, explosions can happen several times within a single frame due to the lack of checks.

To fix this, all you need is a boolean check in the detonation function, it's that simple, OVERKILL has not fixed this until now.