Dynamics context spawns additional contexts when polyphonic

[Valentin Villenave]

Greetings everybody,

I’m having a weird time today with the following code:

%%%%

\version "2.17.30" % Also with earlier versions.

\new Dynamics { a1\f << a \\ b\p >> }

%%%%

The first bar works as expected; in the second all hell breaks loose:
notes are printed in newly-created Voice contexts, and an additional
(unwanted) Staff context is spawned.

I suspect the VoiceSeparator item is the culprit here, since removing
it prevents the behavior from being triggered:

\new Dynamics {
  a1\f
  $(make-simultaneous-music (list
      (make-music 'NoteEvent
        'pitch (ly:make-pitch -1 5 0)
        'duration (ly:make-duration 0 0 1))
       ;(make-music (quote VoiceSeparator))
       (make-music 'NoteEvent
        'pitch (ly:make-pitch -1 6 0)
        'duration (ly:make-duration 0 0 1)
        'articulations (list
          (make-music 'AbsoluteDynamicEvent
           'text "p")))))
}

Any thoughts?

Regards,
Valentin.

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