Strange polyphonic behavior

[Helge Kruse]

I have found a strange behavior with incomplete staves. This is not really important for a complete score, since you usually want to have all staves to have the same number of measures. But while entering the notes I've been surprised that empty staves will be drawn to the end of the piece when a specific pattern is in the music. Here's an example:

\version "2.16.0"

\language "deutsch"

\score {

  \new PianoStaff <<

    \new Staff {

      \key f \major

      \relative c ' {

        << { g'2~g8 e f g } \\ { <d b>2\> c2\! } >> |

        << { g'2~ g8 c <e, g b c> c' } \\ { <b, d f>2 e8  } >>

      }

    }

    \new Staff {

      \clef bass \key f \major

      \repeat unfold 40 { c4 }

    }

  >>

}

Both measures use polyphonic notes as shown at "Double backslash construct" in NR 1.5.2 . In the second measure the second _expression_ is "incomplete". When you comment out the second measure only the lower stave is drawn to the end. The same appears when you add "s s s" after the e8 to fill the second _expression_ of the measure. 

So one could guess that the second _expression_ must have the same length as the first in polyphonic. But when you shorten the c2 in the first measure to c4 nothing similar appears. This is quite strange. Are are any dangerous thing to expect when the first and the second _expression_ of a polyphonic are not at equal length?

Regards

Helge