From http://en.cppreference.com/w/cpp/numeric/random/random_device:
Note that std::random_device may be implemented in terms of a pseudo-random number engine if a non-deterministic source (e.g. a hardware device) is not available to the implementation.
I would expect a decent implementation to at least seed the RNG though.
Edit: I suspect they deliberately chose to deliver the same sequence each time, to make obvious the fact that the stream wasn’t as random as promised.