Minimum length of multi-measure rests?

[Mats Bengtsson]

I tried to increase the minimum length of multi-measure 
rests, but the minimum-length property doesn't work as
I expected. How to do it? Bug?

Example:

\score{\notes\relative c'{
  c1 R1*12 c1 }
\paper{
  linewidth = -1.
  \translator{
    \ScoreContext
    skipBars = ##t
    % Why doesn't this work?
    MultiMeasureRest \override #'minimum-length = #60
  }
}
}


   /Mats