Barcheck errors with Timing.measurePosition and multiple voices

[Nick Payne]

With more than one voice, using Timing.measurePosition for partial bars 
results in spurious barcheck errors and also causes problems with 
automatic beaming:

\relative c'' {
    \time 3/4
<<
        {
            \partial 4.
            c4. |
            c8 c c c c c |
            c c c c c c |
            \set Timing.measurePosition = #(ly:make-moment -3 8)
            c4. |
        }
        \\
        {
            \partial 4.
            c,4. |
            c8 c c c c c |
            c c c c c c |
            \set Timing.measurePosition = #(ly:make-moment -3 8)
            c4. |
        }
>>
}

If instead of using Timing.measurePosition I use Score.measureLength for 
the partial bars, then the barcheck and beaming errors disappear but the 
bar numbering is incorrect with multiple repeat sections:

\relative c'' {
    \time 3/4
    \override Score.BarNumber #'break-visibility = #'#(#t #t #t)
    \repeat volta 2 {
        \partial 4.
        c4. |
        c8 c c c c c |
        \set Score.measureLength = #(ly:make-moment 3 8)
        c4. |
    }
    \repeat volta 2 {
        \set Score.measureLength = #(ly:make-moment 3 8)
        c4. |
        \set Score.measureLength = #(ly:make-moment 3 4)
        c8 c c c c c |
        \set Score.measureLength = #(ly:make-moment 3 8)
        c4. |
    }
}

a.png
Description: PNG image

b.png
Description: PNG image