Syllables not centered under notes after volta

[Eyolf Ostrem]

I've encountered a strange problem:
After a section with volta, the lyrics are not centered under their notes, but 
are instead left-aligned. 

In the following example, the lyrics for textAbgesang are left-aligned. I 
can't see why that should be. Is it a bug, or is there something that I've 
missed?
(a pdf can be found on: http://oestrem.com/salmer/et-trofast-hjerte.pdf)

Eyolf Østrem



\version "2.6.4"
\header {
    title = "Et trofast hjerte, Herre min"
    subtitle = ""
    composer = "Strassburg 1525"
    poet = ""
}

#(set-global-staff-size 23)
\paper {
        indent = 0\cm
        leftmargin = 2.5\cm
        linewidth = 16\cm
        betweensystempadding = 0.8\cm
}

melody = \relative c' {
        \clef treble
        \key g \major
        \time 3/2
        
        %melody:
        \context Voice = stollen {
                        \repeat volta 2 {
                        \partial 2
                        g'2 | fis4 g a2 a | g4 a b2 c |
                        b4 a g2 fis4( g) | a2 g
                        %repeated music
                }
        }
        \context Voice = abgesang {
                %musikk abgesang
                \partial 2
                g2 | a4 c b2 g | a4 fis e2 fis |
                d4 d a'2 b | c4 a g2 d' |
                b4 a g2 fis4( g) |
                a2 g1\fermata \bar "|."
        }
}

textStollenEn = \lyricmode {
        Et tro -- fast hjer -- te, Her -- re min,
        skal dig til re -- de væ -- re,
}

textStollenTo = \lyricmode {
        du mig for -- lø -- ste, jeg er din,
        thi ske dig pris og æ -- re!
}

textAbgesang = \lyricmode {
        Den sag er klar, du kær os har,
        på kor -- set selv vor synd du bar,
        at vi Guds børn må væ -- re.
}

\score { <<
        \context Voice = one {
                \autoBeamOff
                \melody
        }
        \lyricsto "stollen" \context Lyrics = mainlyrics \textStollenEn
        \lyricsto "stollen" \context Lyrics = repeatlyrics \textStollenTo
        \lyricsto "abgesang" \context Lyrics = mainlyrics \textAbgesang
        >>

        \layout {
        }
}



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