symfony/symfony — comment on commit 2e1344eb7ef1e4a6c5cc21e098fd2a6404f2b289
File: src/Symfony/Component/Routing/RouteCollection.php line 219
By fabpot:

Right, and that should not be a problem as a placeholder in a prefix should probably not be used in the embedded routes. And this has the nice side-effect of being able to override the _scheme for all the routes for instance.