Slurs within chords, within tuplets -- seem to be ignored (without warnings!)

[Pete Farmer]

Dear lilypond experts,

This tiny example compiles without warnings or errors, yet the Slurs in the first two measures seem to be ignored.

Measures three and four demonstrate that the issue can be resolved by splitting into separate Voices, and could be cleaned up by tweaking, but as the music is only one voice, this is hardly an improvement.

Can anybody tell me why the interleaved inter-chord inter-tuplet slurs are not appearing? ...and no collision warnings?

-------------<example>----------------

\version "2.18.2"

\score {

 \new Staff {

 \clef "treble_8"

 \key b \minor

  <cis a cis'>4.\arpeggio e'8 ~ e'4 \tuplet 3/2 {b8\rest b8\rest <gis  b( >8}

  \tuplet 3/2 {<a cis')>8 ~ <a cis'>8 <gis( b\(>} \tuplet 3/2 {<a) cis'\)>8 ~ <a cis'>8 <gis b>8}  \tuplet 3/2 {<a cis'>8 ~ <a cis'>8 e'8} b4\rest

 <<

  {

   <cis a cis'>4.\arpeggio e'8 ~ e'4 \tuplet 3/2 {b8\rest b8\rest b(}

    \tuplet 3/2 {cis'8) ~ cis'  b\(} \tuplet 3/2 {cis'8\) ~ cis'  b}  \tuplet 3/2 {cis'8 ~ cis' e'8} b4\rest

  }\\{

   s4. s8 s4 \tuplet 3/2 {s8 s gis(}

   \tuplet 3/2 {a8) ~ a gis(} \tuplet 3/2 {a8) ~ a8 gis(}  \tuplet 3/2 {a8) ~ a r} s4

  }

 >>

 }

}

------------</example>----------

Thank you all, peace and love,

--p