Note that the "co-op partner" also fires a slingshot pallet each time you switch.
I'd still stick with the option I provided of witching the hotkeys for switching characters
I also never got this error, then again I keep using the controller. I didn't actually know I could use multiple powers, they are ALL my left button and the powers only ever worked during the missions associated with them, otherwise I shoot my sling shot. I wish I knew other powers work in other areas, that would have made more parts of the game easier...