Volta lyric clash with multiple staffs

[Roy Rankin]

I am trying to print music for a choir, and on my first attempt
at using lilypond [1.2.0, 1.2.1] have run into the following problem.
When I print multiple staffs, each with a lyric, and have a volta;
the volta spanning bar from a lower staff and the lyric text  from the upper
staff overlay each other.  A script showing the problem appears below.

It would seem that the vertical size of the volta spanning bar is
not taken into account in the vertical spacing. I have tried setting
Score.minVerticalAlign (Commented out in example) but this mostly increases
the space between the staff and its lyrics, not between the lyrics
and the staff below.

Although this problem seems like a bug to me, how can I increase the
spacing between the lyrics and the staff below when using multiple staffs.

Regards,
Roy Rankin


tune = \notes\relative c' {
           \repeat volta 2 { c2 d }
           \alternative { { e1 } { e2 r2 }}
}
words = \lyrics {
        main part repeat1 repeat2
}

\score {

    <
        %\property Score.minVerticalAlign = "30."
        \addlyrics
            \context Staff = "S1" { \$tune }
            < \context Lyrics = "L1" \$words >
        \addlyrics
            \context Staff = "S2" { \$tune }
            < \context Lyrics = "L2" \$words >
    >
    \paper {}
}