saveRouteToCache returns false instead of true when save succeeds (Android)

Version 2.5 JavaDoc says:
public boolean saveRouteToCache(int routeID)
routeID - The id of the route, which can be obtained from SKRouteListener.onRouteCalculationCompleted(SKRouteInfo) 
Returns: true for success false otherwise.

public void loadRouteFromCache(int routeID)
routeID - id of the route.
I calculated a route with 2 alternates and saved them to the cache.

for (int routeId : newRoutes) {
saveRouteToCache Route with ID  2806427 saved to cache  = false
saveRouteToCache Route with ID  7000731 saved to cache  = false
According to the status, it failed, but this works:
loadRouteFromCache with ID = 2806427 from cache 
loadRouteFromCache with ID = 7000731 from cache
What really confused me is that I originally tried the save using the wrong ID and got a success status, even though the routes weren't actually saved:
   for (int i = 0 ; i < newRoutes.size() ; i++) {
   saveRouteToCache Route with ID  0 saved to cache  = true
   saveRouteToCache Route with ID  1 saved to cache  = true