SK53
Unless you describe which of tens of OSM routing products you might be using it's difficult to know. Assuming it's one of the car routing ones on the main website, both routes behave as I would expect a) https://www.openstreetmap.org/directions?engine=mapzen_car&route=51.4382%2C-0.5016%3B51.4354%2C-0.4969#map=18/51.43675/-0.49977; and b) https://www.openstreetmap.org/directions?engine=mapzen_car&route=51.43732%2C-0.49654%3B51.43800%2C-0.49995#map=18/51.43718/-0.49871.

This is a really major junction in the Greater London area; I'd expect it to be festooned with notes if it wasn't routing properly.in most apps.