\grace in repeat breaks volta spanner?

[steve]

  HOwdy!

        I have a problem putting a grace note in a repeat, when there are
two staves
in a system. See this link for a simplified example

http://indra2.web.net/~linuxsui/gooeytar.com/public/lilypond/

http://indra2.web.net/~linuxsui/gooeytar.com/public/lilypond/lily_grace_error.pdf

    This is the error when compiling the source file

GNU LilyPond 2.16.2
Processing `lily_grace_error.ly'
Parsing...
Interpreting music...
warning: already have a volta spanner, ending that one prematurely
[8][8]
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
Layout output to `lily_grace_error.ps'...
Converting to `./lily_grace_error.pdf'...
Success: compilation successfully completed


      Works if there is just one stave. Is there a fix for this?

       This is the lilypond code that the above was created from

\version "2.16.2"

global = {
  \time 3/4
  \clef "G_8"
  \key g \minor
}

guitarone = \relative c {

        \repeat volta 2 { cis2. | }
        \alternative {
            { cis4 r r }
            { cis4 r r }
    }

        \repeat volta 2 { fis2. | }
        \alternative {
            { \grace fis16  g2. |}
            { g2. |}
    }
}

guitarthree = \relative c'  {

        \repeat volta 2 { a2. | }
        \alternative {
            { d2. | }
            { d2. | }
        }

        \repeat volta 2 { d2. | }
        \alternative {
            { g2. |}
            { g2. \bar "|." |}
        }
}

\score {

        \new StaffGroup {
        <<
            \new Staff << \global \guitarone >>
            \new Staff << \global \guitarthree >>
        >>
        }

        \layout { }
}


          Ideas?

         thanx - steve