Forked lightning bug?

From the helpfile: This spell allows an Invoker to channel a forking bolt of lightning into a group of targets or similar creatures. The bolt will fork as many times as necessary to strike all who are associated with the initial target. However, this happened: Victim yells 'Heelp ssoomeeoonee iiss aattaackiing mee!' A bolt of forked lightning shoots forth from your hands! You fade into existence. Your forked lightning MASSACRES Victim! The gods protect Groupmate1. The gods protect Groupmate2. Your forked lightning === OBLITERATES === a bystander mob! You hear the sizzling pop of electrical arcs raging across another bystander mob! Your forked lightning *** DEVASTATES *** another bystander mob! Their group was even fighting the first bystander mob, and they certainly weren't "associated" with the first target in any manner. The second bystander mob was a complete outsider. This doesn't happen when attacking a mob; the spell remains contained. If this is somehow by design, then please at least add a remark about it in the helpfile?