Simon says: "Outside of section 5, header faulting is not handled correctly [it will generate a mustUnderstand fault, even if the header is not targeted at the ultimate destination]".

Actually, we leave it to the app developer to decide because actor resolution is such a sticky issue. They can set the DidUnderstand property to true, and then we won't fault. Otherwise, we err on the side of caution and fault.

BTW: aren't sparse arrays the same as partial arrays?