Invoker 6pc Bonus interacting with Simplicity's Strength and Depth Diggers

It appears that the 6pc bonus for the Crusader Invoker set is getting modified by Simplicity's Strength and Depth Diggers, which both modify damage from Primary skills. It does not interact this way in game; I suspect it's a symptom of the Thorns damage being applied to Punish's / Slash's damage rather than a separate effect.