slurs in polyphony and TabStaff problems

[Federico Bruni]

Another report about slurs and TabStaff.
IIUC, now slurs connect note heads in polyphony (instead of stems).
I _think_ that it's a desired output.

However, it's breaking the TabStaff slurs.
Find attached .png examples (see differences between 2.14.2 and 2.15.40).

here's the minimal example:

\version "2.15.40"

first =  \relative c' {
  b8( c)
}

second = \relative c {
  d8( e)
}

\score {
  \new StaffGroup <<
    \new Staff = "guitar" <<
      \context Voice = "first voice" { \clef "G_8" \voiceOne  \first }
      \context Voice = "second voice" { \clef "G_8" \voiceTwo  \second }
    >>
    \new TabStaff = "tab" <<
      \context TabVoice = "tab first voice" { \clef "moderntab" 
\voiceOne \first }
      \context TabVoice = "tab second voice" { \clef "moderntab" 
\voiceTwo \second }
    >>
  >>
}

tab-slur-bug.2.14.2.png
Description: PNG image

tab-slur-bug.2.15.40.png
Description: PNG image