OK... there is a bit in documentation:

_Note: to ensure a route is properly connected when using a two alternative directions (alternative route A1 and A2, using the Role forward and Role backward roles), make sure the element before the branch connects to the first element in A1 and the element after the branch connects to the last element of A2. Also note that the Role forward and Role backward roles refer to the directionality of the ways in A1 which need to be going in the same direction; if not all ways in A1 run in the same direction it may be necessary to use both Role forward and Role backward for the same alternate route A1._

which is not very clear.  However using JOSM Editor it makes some sense as it is explain how to do those part of a linear path that in places has two choices. 

Getting these portions (with two routing options) correctly ordered requires the forward/backward Role to be right. 

https://hiking.waymarkedtrails.org/#?map=15.0/56.2041/-2.7687 

Let me know if I am missing something? 