Hi, I'm having the same issue, I never changed the bones and all of a sudden the right hand holds the lightsaber backwards. The hand bone is the same to any non modded model. I tried flipping the right to match left and it still held it the same way. The only real change was adding a new object in the hirearchy, could that somehow break the bones? very weird bug. I'm using blender btw. It's the first time this happens.