instantiating voices

[Hugh Myers]

The 2.10 manual says that:

<< \upper \\ \lower >>

is equivalent to

<<
  \new Voice = "1" { \voiceOne \upper }
  \new Voice = "2" { \voiceTwo \lower }
>>

Which in simple situations seems true enough. However as soon as
tablature is added the above is broken; for example:

\version "2.13.7"

firstPolyRepeatV = {
  <<
  { r4 \times 2/3 {gis 8 b e } e,4 \times 2/3 {gis8 b e} e,2 } \\ { e,2.~e }
%     \new Voice = "1" { \voiceOne { r4 \times 2/3 {gis 8 b e } e,4
\times 2/3 {gis8 b e} e,2 } }
%     \new Voice = "2" { \voiceTwo { e,2.~e } }
  >>
}
{

  <<
    \time 3/4
    \set Score.barNumberVisibility = #all-bar-numbers-visible
    \bar ""
    \set Score.voltaSpannerDuration = #(ly:make-moment 3 4)
    \new Staff \relative c'' {
      \firstPolyRepeatV
    }
    \new TabStaff \relative c' {
      \firstPolyRepeatV
    }
  >>

}

The shorthand for << \\ >> works as intended while the explicit
voicing fails. Work arounds?

--hsm