If you set it too low or with too many bounces, it will expand exponentially and have a ridiculous amount of damage. I've never seen it actually bug though.
Example: we have a 200 damage lightning with -1 decay, and 7 bounces. 200, 400, 800, 1600, 3200, 6400, 12800, and you're at enough damage to kill the strongest heroes, from 200 damage... Chain lightning gets out of hand quickly when you make it grow, so be careful.