E90 Bumper Replacement Question

Has anyone had work done in which they had to remove the rear bumper? I was hit on my rear drivers side door and in order to replace the door and paint it they had to remove the bumper. Well I recieved a call from the body shop and they told me that they needed to order a new bumper b/c the way the e90s were designed was when the rear bumpers are removed they have to be replaced with a new bumper! The only reason I could see this as true if it had something to due with the airbags or crash protection. I'm not paying for it (insurance).

F.Y.I. It was not a BMW dealer's body shop, it was a shop that BMW referred me to.

If the rear bumper is removed it has to be replaced with a new bumper? I'm not sure what kind of special bumpers BMW uses, but it sounds kind of fishy to me. I'm guessing the shop most likely removed the bumpers in an improper manner and damaged the bumper. Then again, they may be super bumpers... I'm no BMW bumper expert. Any second opinions? Oh by the way, do you think I said bumper enough times?