Colin,
When creating a route, there is a section at the top of the page labeled "Auto Plot" with options of "off, By Road, On Foot, By Bike" to create a route that has both public roads and foot paths this option should be "Off" so you can meander off public roads and onto footpaths or trails. If the "By Road" is on the route will be redirected to the closest public roadway and not where you are trying to go. Hope this Helps.
I want to map my own route on road/ footpaths, but on a certain point it will either follow the road or choose its own route in a different direction to the point where I am trying to send the route.
I have tried this several times, changing the route in a clockwise direction, trying to drag it, but nothing works.
So it looks like I will be going back to the old fashion way of using a paper map & working out my routes now.