percent repeat does not work with multiple (drum)voices

[Corien Prins]

> I'm not top posting.

% When percent repeat is used in drummode, all output in the 
% same score after the repeat is messed up: the different voices
% creat their own staff with a different clef. 
% When 'percent' is replaced by 'unfold' or 'volta' it works fine. 


\paper{ ragged-right=##t }
\version "2.12.1"

\score {
   \new DrumStaff << 
      \new DrumVoice = "1" { s1 *2 }
      \new DrumVoice = "2" { s1 *2 }
      \drummode {
         \repeat percent 2 {
            << {hh8 hh hh hh hh hh hh hh|} \\ {bd4 sn bd sn|} >>
            << {hh8 hh hh hh hh hh hh hh|} \\ {bd4 sn bd sn8 bd8|} >>
         }
         << {hh8 hh hh hh hh hh hh hh|} \\ {bd4 sn bd sn|} >>
         << {hh8 hh hh hh s2|} \\ {bd4 sn sn16 sn sn sn sn16 sn sn sn |} >>
      }
   >>  
}