Thankyou, that's along the lines of what I am looking for.

I've been trying to research this myself and keep drawing blanks as to the actual reason.

If it's a regulation, it would be great to have a link to it.

I guess this is the sort of thing that goes along the lines of:

Q. Why is it done like that?

A. Because that is the way it's supposed to happen!

Q. Why is that the way it's supposed to happen?

A. Because that's simply the way it's done!