spacing with arpeggio

[Kieren MacMillan]

Hi all,

This [reasonably-minimal] snippet shows a bug that's biting me a lot in my 
current engraving.

Thanks,
Kieren.
_______________________

\version "2.17"
\language "english"

global = {
  \time 6/8
  \key d \dorian
  s8*6*2
}

pfNotesUpper = \relative a' {
  <<
    { \voiceOne
      <a>8\arpeggio g a <bf>\arpeggio c d
      <a e'>4.\arpeggio <a e'>4\arpeggio f'16 e
    }
    \new Voice { \voiceTwo
      d,4. c
      <cs d> <cs d>
    }
  >>
}

pfNotesLower = \relative a {
  \clef bass
  <<
    { \voiceOne
      a8 d, e f4.
      e e
    }
    \new Voice { \voiceTwo
      <bf>\arpeggio <a>4\arpeggio g8
      <a>4.\arpeggio <a>\arpeggio
    }
  >>
}

\score {
  \new PianoStaff = "pf" \with { connectArpeggios = ##t } <<
      \new Staff = "pfUpper" << \global \pfNotesUpper >>
      \new Staff = "pfLower" << \global \pfNotesLower >>
  >>
}