That produced a slight change.
With MC on the Start tab, the only tab open, when I closed it, then on restarting MC using "/Mode Windowed" the Cover Art showed up when I used Ctrl+P to start playback. It should have been one of the Visualizations though.
With MC on Playing Now when I closed it, Cover Art didn't display when I started playback.
So the right idea, but still not the answer.
Is there no way to tell what owns the Display? An MCWS command or similar?
I tried
http://localhost:52199/MCWS/v1/Playback/Info?Zone=-1 which gave:
<Response Status="OK">
<Item Name="ZoneID">0</Item>
<Item Name="State">2</Item>
<Item Name="FileKey">6456</Item>
<Item Name="NextFileKey">6457</Item>
<Item Name="PositionMS">73499</Item>
<Item Name="DurationMS">330533</Item>
<Item Name="ElapsedTimeDisplay">1:13</Item>
<Item Name="RemainingTimeDisplay">-4:17</Item>
<Item Name="TotalTimeDisplay">5:30</Item>
<Item Name="PositionDisplay">1:13 / 5:30</Item>
<Item Name="PlayingNowPosition">0</Item>
<Item Name="PlayingNowTracks">32</Item>
<Item Name="PlayingNowPositionDisplay">1 of 32</Item>
<Item Name="PlayingNowChangeCounter">2</Item>
<Item Name="Bitrate">1015</Item>
<Item Name="Bitdepth">16</Item>
<Item Name="SampleRate">44100</Item>
<Item Name="Channels">2</Item>
<Item Name="Chapter">0</Item>
<Item Name="Volume">0.28</Item>
<Item Name="VolumeDisplay">28% (-26.0 dB)</Item>
<Item Name="ImageURL">MCWS/v1/File/GetImage?File=6456</Item>
<Item Name="Artist">Pet Shop Boys</Item>
<Item Name="Album">Actually</Item>
<Item Name="Name">One More Chance</Item>
<Item Name="Status">Playing</Item>
</Response>
Also
http://localhost:52199/MCWS/v1/UserInterface/Info which gave:
<Response Status="OK">
<Item Name="Mode">2</Item>
<Item Name="InternalMode">-996</Item>
</Response>
Maybe that internal mode means something?