Routes not clearing

[GarySN]

Recently I've encountered an intermittent problem whereby the route being worked on is not redrawn when the waypoints change, or even when starting a new route.  This results in odd-looking routes, as shown in the attached screendump.  I had just changed the final waypoint from Llanberis to BeddGelert, and ended up with the route drawn as shown.  In an attempt clear the route altogether, I clicked File --> New, which is why the screendump shows an empty waypoint list, yet still the route as drawn persisted.

Is there a way to force the route to redraw?