Hi Super,
This is a known bug. In the current build you have to manually fix this each time your co-op partner joins the game (this occurs every time you load a game as well). To manually fix it, you will need to talk to the NPC that you want your co-op partner to control and "dismiss" them from the party. When you do this, the NPC will either go back to the tavern or (if you have it unlocked) they will go back to your dimensional house. Have your co-op partner travel to the NPC and invite them back into the party and they will be chained properly. It's a painful work-around until they get the overall issue fixed.
-tech
Last edited by techn0logic; 25/03/14 04:59 PM.