Lyric with tie over repeat seems to be messing things up

[Tim Rowe]

I've tried to reduce this as much as I can, but if I change almost
anything the effect goes away.

My problem is, in the score below the tied note on the lyric "x" seems
to be forcing a spurious repeat bar. If I comment out the lyrics
everything is fine. If I \skip to the end of the bar "x" ties into
*and* get rid of the tie at the end of that bar then everything is
fine, but when I put that tie back in I get *two* spurious bars.

What am I doing wrong here, and how do I fix it?

Thanks. Markup follows.

\version "2.12.3"

soprano = \relative c'
{
  \clef treble
  \key bes \major
  \time 4/4
  \partial 8 c8 |
  \repeat volta 2
  {
    c4 c8 c~ c4 c8 c~ |
    %c2. r8 c |
    c4 c8 c~ c4 c8 c~ |
    c4. c8 c c16 c~ c c c8~ |
    c4~ c8. c16 c8 c16 c~ c c c8~ |
    c2. c8 c~ |
  }
  c2 r8 c c8. c16~ |
  c2 r8 c c8. c16~ |
}

one = \lyricmode {
  \repeat volta 2
  {
    \repeat volta 2
    {
      A b c d e f
      g h i j k l
      m n p p q r
      s t u v w x
    }
  }
}

\score {
  <<
    \new Staff <<
    \new Voice = "one" { \soprano }
    >>
    \new Lyrics \lyricsto "one" { \one }
  >>
  \layout { }
}


-- 
Tim Rowe