\version "2.17.24"

\header{
  title = "Stemless notes & slurs"
}

\markup{I expect all the other examples to produce output like this one produces. Am I wrong?}
\score {
  \relative c'' {
    \override Stem #'transparent = ##t
    \override Stem #'Y-extent = ##f
    
    \stemDown
    a4( d)
  }
}

\score {
  \relative c'' {
    \override Stem #'transparent = ##t
    \override Stem #'Y-extent = #'(0 . 0)
    
    a4( d)
  }
}

\score {
  \relative c'' {
    \override Stem #'transparent = ##t
    \override Stem #'Y-extent = ##f
    
    a4( d)
  }
}

\score {
  \relative c'' {
    \override Stem #'stencil = ##f
    
    a4( d)
  }
}

\score {
  \relative c'' {
    a4( d)
  }
  \layout {
    \context {
      \Voice
      \remove "Stem_engraver"
    }
  }
}