Mindshackle Scarabs and Kharn the Betrayer

Here's a question for you.  I'm running Kharn the Betrayer as one of my HQ choices.  He's a nasty Khorne guy who really doesn't mind from where the blood flows -- just so long as it flows.  In close combat there's a chance he'll hit his own allies. Mindshackle scarabs in the new necron rules are an interesting entry.  Fail a Ld test on 3d6 and the enemy strikes their own allies.  How does this