Force barline in middle of a bar

[Jethro Van Thuyne]

In my (minimal) example below, I'm having trouble with displaying
dashed barlines in the middle of the bar. Probably the first
occurance of the tuplets in the violin - a figure which is running
'through' the bar - is making things difficult, but is there a way
to force the barline anyway? I don't get any errors while parsing,
using 2.17.14, but I don't get the dashed barlines either.

Jethro


==== SAMPLE =====

violin = \relative c'
  {
  \time 17/8
  r4 r8 \times 2/3 { a8[ a a] } \times 2/3 { a2 a4 } a2 a4 r4 |
  }

viola = \relative c'
  {
  \time 17/8 
  a8[ a] a4 \bar "dashed" s8 s2 s2 s4 \bar "dashed" a8[ a] |
  }

cello = \relative c'
  {
  \time 17/8
  \times 2/3 { a8[ a a] } a4 \bar "dashed" s8 s2 s2 s4 \bar "dashed" a8[ a] |
  }

\score  
  {
  \new StaffGroup
    <<  
      \new Staff \violin
      \new Staff \viola
      \new Staff \cello
    >>  
  }