Error when "Undo shipment"

"You cannot undo line 10000 because warehouse shipment lines have already been posted"

We have designed it so that you have to delete the posted Whse shipment if you want to undo the sales shipment.   When trying to undo a sales shipment - The message: "you cannot undo the "line xx" because a Whse shipment line has already been posted", is a warning for someone who is undoing something that is in fact not undoable (if the goods have been sent!). The fact that you have to delete the Whse shipment represents a kind of stressing that it's something important, some physical work has been made and you are undoing it.”
from "Undo Shipment" scenario