The situation can be illustrated by a few pictures.
After i put a gun under his right hand
As you can see, when I select spine.003, its position is now located at the gun. When I try to rotate the spine, it will use that gun position as a pivot point, which is definitely unintended. And after I delete the gun, the spine's position goes back, and everything is fine again.
Strangely enough, the breast position remains unaffected, while only the spine is affected. Why is this happening?

