Not sure if it's a bug or not. I almost would guess its not because its something associated with the tree? But maybe it is and the value is supposed to be set to zero if you mess with the world gen.
Steps to Reproduce
Start a new game, no mods, scorpions and snakes set to none in the world gen options. Start burning claw palms with a torch. They each can drop 1 or 2 snakes or scorpions. Not all of them will.
This issue has not been confirmed by a developer yet.