rest under a beam with voiceTwo.ly

[Luc]

% In a Calypso I use beams which connect notes of different duration and 
also with a rest between them to visualise quarters.

In a normal context (measure 1) the rest avoids the collision with the beam.

In a polyphonic context with \voiceTwo, rests are moved down a few spaces 
(measure 2) except for the one under the beam (measure 3) which remains in 
its original, normal or \oneVoice positon.

Explicitly positioning (measure 4) the rest on a pitch does not help.

How can I alter this?

\version "2.8.6"                 % on windows XP

\layout {ragged-right = ##t}

{
g8-"normal" r8 b r a8[ r16 d'] r4 \break    %1
\voiceTwo
g8-"\voiceTwo without beam" r8 b r a8 r16 d' r4 |  %2
g8-"\voiceTwo with beam" r8 b r a8[ r16 d'] r4 |    %3
g8-"\voiceTwo with beam and pitched rests" g8 \rest b g8 \rest a8[ g16 
\rest d'] g4 \rest %4
}