barcheck warning when using Timing.measurePosition in polyphonic music

[Federico Bruni]

Hi,

just a nitpick...

In NR 1.2.3, Upbeats, Known issues and warnings
\set Timing.measurePosition is recommended instead of \partial when the 
partial measure occurs after the beginning of the piece.

Single voice music compiles fine and without warnings:

\version "2.15.36"

\relative c'' {
  \time 4/4
  \partial 2 g2 |
  g1 |
  \set Timing.measurePosition = #(ly:make-moment -2 4)
  g2 |
  g1 |
}


Polyphonic music compiles fine but I get a barcheck warning:

\version "2.15.36"

\new Staff <<
  \new Voice = "first" \relative c'' {
    \time 4/4
    \partial 2 g2 |
    g1 |
    \set Timing.measurePosition = #(ly:make-moment -2 4)
    g2 |
    g1 |
  }

  \new Voice= "second" \relative c' {
    \time 4/4
    \partial 2
    c2 |
    c1 |
    \set Timing.measurePosition = #(ly:make-moment -2 4)
    c2 |
    c1 |
  }
>>

The warning is:
warning: barcheck failed at: -1/2