System-stretch do not work with system-count

[Rune Zedeler]

If system-count is set then system-stretching does not take place:

\version "2.11.41"
mel = \repeat unfold 64 a'32
\paper {
  ragged-last-bottom = ##f
  system-count = #2 % works if this line is commented out
}
\layout {
  \context {
    \Score
    \override VerticalAlignment #'max-stretch = #30
  }
}
\score {
  \new ChoirStaff << \mel \mel \mel \mel \mel >>
}


The system-count line should not do anything, because lilypond generates 
2 sytems nevertheless. BUT, when the line is present, then the 
VerticalAlignment stops working.
Attached two pictures. One where the line is commented out, and one 
where it is not.

-Rune