I really hate to bump posts when I was the last one to post, but I really need a solution here.
I am unsure why Auto Attack is giving me so many issues. The player getting stuck when there is nothing to attack seems like it could be a bug. It only happens if Auto Attack is enabled on the combatant, and it happens regardless of the option being enabled or not in the Group Target settings.
Since I want to make sure that a Click to Attack feature is implemented, I should probably describe in more detail what I am trying to accomplish. From playing Torchlight II, here is what we need. When you click the mouse on anything that isn't an NPC or an enemy, you should move to that location. If you click on an NPC, you should move to them and initiate conversation. If you click on an enemy, you should attack them. Torchlight II also has options for allowing you to do stay still and attack, regardless of target, by holding Shift while clicking. It also has an option to only move or attack if there is a target if Ctrl is held when clicking. Also of note, if the player isn't clicking, then their character should do nothing, even if they had targeted an enemy and attacked it. Basically they should only attack if clicked on, not continue automatically.
I know the above is a bit complex. At the very least, we would like the clicking without modifier keys to function as above. At the moment, movement with clicking is working fine. I have not yet tried to see if clicking an NPC can start a conversation with them, but the Group Target + Auto Attack method is just not working out for me. I need something more like explained above.