#'stencil vs. #'transparent

[Daniel Rosen]

I'm typesetting a piece of vocal music, and I want to have a melisma without a 
slur being drawn. I tried \override Slur #'stencil = ##f, but when I compiled 
it, the output appeared as if I had written \override Slur #'transparent = 
##t--in other words, it occupies space, contrary to the description of the 
stencil property at 
http://www.lilypond.org/doc/v2.16/Documentation/notation/visibility-of-objects. 
Is this a bug? If not, what am I doing wrong? If so, how can I get around it? 
(I can't use \slurUp because that would change the position of any grobs that 
appear above the staff--the MetronomeMark in the examples below, but also 
DynamicTexts and certain Scripts like fermatas.)

%%% start

\version "2.16.1"
slurMusic = \relative c' { c1( | d2 c | e1) | }
noSlurMusic = \relative c' { c1 | d2 c | e1 | }
lyric = \lyricmode { Lyric }

<<
  \new Voice = "voice" { \tempo "default" \slurMusic }
  \new Lyrics \lyricsto "voice" { \lyric }
>>

<<
  \new Voice = "voice" { \override Slur #'stencil = ##f \tempo "#'stencil = 
##f" \slurMusic }
  \new Lyrics \lyricsto "voice" { \lyric }
>>

<<
  \new Voice = "voice" { \override Slur #'transparent = ##t \tempo 
"#'transparent = ##t" \slurMusic }
  \new Lyrics \lyricsto "voice" { \lyric }
>>

<<
  \new Voice = "voice" { \tempo "no melisma" \noSlurMusic }
  \new Lyrics \lyricsto "voice" { \lyric }
>>

%%% end

DR