Adding a new vertex works as described in section 4 of Route Tracks:
**but** only the first time a new vertex is added.
The only way to add another vertex anywhere on the same track is to select a different track (on a different net) and then go back to the original track. Double clicking on it then adds another vertex.
Happening on online version in Chromium in Linux Mint 18.3
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
