a problem with timing_engraver & barlines

[Thorkil Wolvendans]

Hi list,
I'm typesetting a polymetrical piece for 2 pianos, in which Piano 1 has a 
different timesignature than Piano 2.
I need to make a score in where one pianopart below the other. This works 
very well by changing the timing_engraver from the Score context to the 
PianoStaff context, there's only one problem:
Both piano's have occasionally double barlines, but the double barlines of 
Piano 2 are visible in the Piano1-part instead of in the Piano2-part.

I included an example to show the problem.
When processed, notice in the last bar the double barline in Piano 1, which 
should be in Piano 2.

Can someone help me?

Regards,
Thorkil

%%%START EXAMPLE %%%

i = \relative c'{
\time 1/4
\repeat unfold 8 {f16 as d as}\bar"||"
\repeat unfold 6 {f a c d}} %here is no \bar"||" written, yet displayed

ii = \relative c'{
\time 1/4
\repeat unfold 14 {c16 e g e}}

iii = \relative c''{
\time 7/16
\repeat unfold  8 {c,16[ e gis] c,[ e gis] es}\bar"||"} %this doulbe 
barline is placed in the Piano1-part!

iiii = \relative c''{
\time 7/16
\repeat unfold  8 {g16[ a b] c[ g a] b}
}

pianoi = {
        \context PianoStaff <<
     \set PianoStaff.instrument = "Piano I  "
        \context Staff = "right" <<
     \i
        >>
    \context Staff = "left" <<
     \ii
    >>
  >>
}
pianoii = {
        \context PianoStaff <<
     \set PianoStaff.instrument = "Piano II  "
        \context Staff = "right" <<
     \iii
        >>
    \context Staff = "left" <<
     \iiii
    >>
  >>
}

\score {
  \context StaffGroup = Pianos <<
        \context PianoStaff = "pianoi" <<
         \set PianoStaff.instr = "I "
         \pianoi
        >>
        \context PianoStaff = "pianoii" <<
         \set PianoStaff.instr = "II  "
         \pianoii
        >>
  >>
 \layout{
        \context{
            \Score
            \remove "Timing_engraver"
        }
        \context{
            \PianoStaff
            \consists "Timing_engraver"
        }
  }
}
%%% END EXAMPLE %%%