Lilypond "elevation" of rests after two voice passage

Question

After I resolve a two voice passage that involves using \set associatedVoice, rests for the remainder of the piece are higher on the staff than before:

The eighth rest at the beginning is lower on the staff than the quarter rest at the end. In my longer piece, this persists until the end, several pages later, regardless of where the notes on the staff stand. How do I convince the rests to return to their beginning latitude? Here's the Lilypond markup for the above example:

\version "2.19.12"
\language english

global = {
  \clef treble
  \key c \major
  \time 4/4
  \tempo 4=120
}

vocalNotes = \relative c' {
  \global
  c8 r8 d4 e f | %1
  g a
  << {\voiceOne b16 c d e }
     \new Voice = "alternative" {\autoBeamOff \voiceTwo b4 } >>
  d4 | %2
  c2 r4 c4 | %3
}

textVerseOne = \lyricmode {
  \set stanza = #"1. "
  This8 \skip8 is4 a text. | %1
  Here4 it4 goes16 ve -- ry fast and4 | %2
  ends.2 \skip4 ends.4 | %3
}

textVerseTwo = \lyricmode {
  \set stanza = #"2. "
  A8 \skip8 se4 -- cond text, | %1
  and4 it \set associatedVoice = "alternative" slows4
  \set associatedVoice = "vocalMelody" and4 |
  ends.2 \skip4 ends4 |
}

\score {
  <<
  \new Voice = "vocalMelody" {\autoBeamOff \vocalNotes }
  \new Lyrics \lyricmode { \textVerseOne }
  \new Lyrics \lyricmode { \textVerseTwo }
  >>
}

Answer 1

Your parallel passage does not introduce a Voice for the upper part, you wrote:

  << {\voiceOne b16 c d e }
     \new Voice = "alternative" {\autoBeamOff \voiceTwo b4 } >>

So the \voiceOne will persist in its effect on the surrounding Voice until the end of its reign. You should be using

  << {\voiceOne b16 c d e \oneVoice }
     \new Voice = "alternative" {\autoBeamOff \voiceTwo b4 } >>

to switch the stem directions and rest positions back to single-voice settings at the end of the passage.