Wrong order of staffs in score

[Ruud van Silfhout]

With the score below I get the staffs in the wrong order. Although it is 
specified that the pianostaff should appear before the pedal staff (as 
for organ-scores), it appears with the pedal staff first and then the 
piano staff. I vaguely remember to have run into such a problem before, 
but I have a new PC without the old information on it and, as said 
before, I cannot reach lists.gnu.org (I get access denied errors).
Still running lily 2.4.3 on cygwin (XP)

TIA,
Ruud
Mutopia maintainer

\score {
 \context GrandStaff <<
   \context PianoStaff = "piano" <<
     \context Staff = "treble" <<
       {c''1}
     >>   
     \context Staff = "bass" <<
       {c''1}
     >>  
   >>
   \context Staff = "pedal" <<
     {c''1}
   >>  
 >>
}