Wielding code. (not dual wield) and bind hands

I was having trouble with a binder thief. I wanted my instrument to stay in my hands NOT MY WEAPON. The instrument wouldn't stay. So I wore a shield, hoping that would get disarmed instead of my instrument. It didn't. So finally I go into battle wearing only my instrument. And get bind hands again... Why is it that you cannot wear an instrument, period, or anything held for that matter, when bind hands is used, but it will let you wear a weapon OR a shield? I want to not have my instrument stolen just because I got jacked by a binder...