`mplay` doesn't work once it has been closed

[Datseris]

MWE

julia> using MIDI, Mplay

julia> mplay(testmidi())
Note retriggered
Note retriggered

julia> mplay(testmidi())
midi: cannot open MIDI output

Julia has exited. Press Enter to start a new session.

So, open the GUI through mplay, and then close it (normally close the window, press the X button at top right). If you try to open mplay again, it doesn't work.