The shuffle problem is reproducable:
Put a huge amount of titles into the default playlist.
Play in shuffle mode, everything is ok.
Play other content, for example a podcast or internet radio.
Select the default playlist again and play in shuffle mode.
The playlist has only 60 tracks after that.
If I clear the playlist and refill, everything works ok, until
doing the above.

Mediabox becomes very slow with huge playlists. Even
returning to the shelf takes a long load.