Groveway national speed limit signs

The area along the Groveway, Walton Hall (OU) side has a lamppost with a double sided “National Speed Limit applies” road sign so actually renders the zone a bit pointless as the stretch going west isn’t then covered by the 40 zone as you’ve exited it. To the East you’ve got 300 meters or so before you officially pass more signs. Very confusing if you pay attention to road signs and might explain why cars are still dangerously hammering it along there. Plus their “get out of jail” card is gifted to them whilst this road sign remains.