How to end a melisma

[pkarl]

I'm trying to figure out the correct way to have LilyPond, v2.19.53, 
generate the attached score, which is for an instrument and a singer, 
but the singer doesn't sing all the notes that the instrumentalist 
plays. Furthermore, the last thing before the singer tacet's is a melisma.

My first naive attempt was:

Music = \relative c'' { c4 d e f    c d e f    r d e f    c d e f }
Lyrics = \lyricmode { do re mi fa __ _ _ _ _
        \repeat unfold 3 { \skip 1 } sol la ti do }
\score {
    \new Staff \Music
        \addlyrics \Lyrics
}

But this generates an extension line that goes right through the rest 
and the next three notes.  It almost seems that the \skip command has 
two conflicting duties:  to indicate the extension of a melisma and to 
indicate that a note should be skipped lyrically.

My next naive attempt was, with the same score block as above:

Music = \relative c'' { c4 d e f    \melisma c d e f \melismaEnd
                        r d e f    c d e f }
Lyrics = \lyricmode { do re mi fa __
        \repeat unfold 3 { \skip 1 } sol la ti do }

but the output is the same, i.e., the extension line goes right through 
the rest and the remainder of the tacet measure.

My next naive attempt was to try to positively indicate where the 
melisma should end:

Music = \relative c'' { c4 d e f    c d e f    r d e f    c d e f }
Lyrics = \lyricmode { do re mi fa __ _ _ _ _  " "
                      \repeat unfold 2 { \skip 1 } sol la ti do }

But that didn't work either.

What did work was to change the single blank to two blanks:

Lyrics = \lyricmode { do re mi fa __ _ _ _ _  "  "
                      \repeat unfold 2 { \skip 1 } sol la ti do }

Can anyone tell me what the correct way is to terminate the melisma 
extension line before a tacet measure?

Screen Shot 2017-10-31 at 11.39.41 AM.png
Description: PNG image