MPRIS player properties are reported with initial values when retrieving them

While playing a music track via the music-app

$ phablet@ubuntu-phablet:~$ gdbus call -e -d core.ubuntu.media.Service -o /org/mpris/MediaPlayer2 -m org.freedesktop.DBus.Properties.GetAll 'org.mpris.MediaPlayer2.Player'
({'AudioStreamRole': <int16 2>, 'CanControl': <true>, 'CanGoNext': <false>, 'CanGoPrevious': <false>, 'CanPause': <true>, 'CanPlay': <true>, 'CanSeek': <true>, 'Duration': <int64 0>, 'Lifetime': <int16 0>, 'LoopStatus': <'None'>, 'MaximumRate': <1.0>, 'MinimumRate': <1.0>, 'Orientation': <int16 0>, 'PlaybackRate': <1.0>, 'PlaybackStatus': <'Playing'>, 'Position': <int64 0>, 'Shuffle': <false>, 'TypedLoopStatus': <int16 0>, 'TypedPlaybackStatus': <int16 0>},)

Properties Position and Duration are zero but should have a value.

With

 $ dbus-monitor --session

I see the property Position being updated as the track is being played.