When creating a route, if you make a mistake and use ‘undo’ button, that does remove the visual line and in distance counter. However, the mile markers remain. If you then click to add a next point, the distance of the new segment seems to get added to the distance that was previously removed.
I can confirm this behavior, but only if I undo back to the start of the route - mid-route undos worked Ok for me in my test, but if I undid everything back to where the starting point was the only waypoint remaining, it did what Marty describes