\shiftOn \shiftOff bug?

[Mark Polesky]

Removing the poylphonic shift for voice 3 automatically
removes the shift for voice 4 and vice versa.  Is this the
expected behavior, or is this a bug?

- Mark

* * * * * * * * * *

\version "2.13.22"

\new Staff \relative c'' {
  \time 2/4
  <<
    { f2 }
    \\ { g,2 }
    \\ { d'2 }
    \\ { b2 }
  >>

  %% removing the default shift in v.3 removes it in v.4...
  <<
    { f'2 }
    \\ { g,2 }
    \\ { \shiftOff d'2 }
    \\ { b2 }
  >>

  %% ...even if \shiftOn is manually added to v.4
  <<
    { f'2 }
    \\ { g,2 }
    \\ { \shiftOff d'2 }
    \\ { \shiftOn b2 }
  >>

  %% and vice versa
  <<
    { f'2 }
    \\ { g,2 }
    \\ { d'2 }
    \\ { \shiftOff b2 }
  >>

  <<
    { f'2 }
    \\ { g,2 }
    \\ { \shiftOn d'2 }
    \\ { \shiftOff b2 }
  >>
}