Polymetric spacing bug

[Michael Käppler]

Though polymetric notation is documented to work, it sometimes leads to 
unexpected page overflow.
Then again, with other time signature combinations, it works very well. 
What is the reason for this
variable behaviour?

See the following example:

\version "2.13.40"
\include "deutsch.ly"

stimmeI = {
  \clef treble
<<
    \relative c'' {
      \time 3/4
      \repeat unfold 9 {
        a4 a a
      }
    }
>>
}

stimmeII = {
  \clef treble
<<
    \relative c'' {
      \time 7/8
      \repeat unfold 8 {
        g8 g g g g g g
      }
    }
>>
}

\score {
<<
    \new StaffGroup <<
      \new Staff \stimmeI
      \new Staff \stimmeII
>>
>>
  \layout {
    \context {
      \Score
      \remove "Timing_translator"
      \remove "Default_bar_line_engraver"
    }
    \context {
      \Staff
      \consists "Timing_translator"
      \consists "Default_bar_line_engraver"
    }
  }
}

Regards,
Michael