If you don't give Simulacrums orders, can they act on their own? Do they have their own personalities, or are they merely your puppets?

In the Icewind Dale games, the Drow wizard Malavon created a Simulacrum, whom everyone thought was him in the first game. It went insane and acted on its own. So is that a unique circumstances, or could you allow a Simulacrum autonomy?