Colliding rests warning

[Nick Payne]

I can't seem to eradicate this warning in single staff polyphony. Here's the
first couple of bars of a Weiss Tombeau. If I have rests in two voices,
Lilypond is warning about too many colliding rests. Doesn't matter if I just
put them as rests and let LP place them where it wants (which doesn't give
the output I want, as it combines the rests) or if I explicitly place them
to indicate a rest in both voices.

I couldn't find anything in the documentation. I found something in the
mailing list archives indicating that the warning shouldn't happen if you
let Lilypond position the rests, but that isn't happening here:

%===========================================================================
========
\version "2.12"

offset = #(define-music-function (parser location type move) (string? pair?)
#{
        \once \override $type #'extra-offset = #$move
#})

#(define RH rightHandFinger)

fingering = {
        \override Fingering #'staff-padding = #'()      
        \override StringNumber #'staff-padding = #'()   
        \set fingeringOrientations = #'(left)
        \set strokeFingerOrientations = #'(right)
        \set stringNumberOrientations = #'(down)
}

treble = \relative c {
        \fingering
        \override NoteColumn #'ignore-collision = ##t 
        
        \repeat volta 2 {
                \offset "TextScript" #'(-7.5 . -2.5)
                        s2.._\markup\bold{\circle {6}=D} <b'-\RH #3 >8 |
                        b8. <e-\RH #3 >16 e8. <g-2-\RH #3 >16 g8. <b-4-\RH
#3 >16 
                        b8[ \acciaccatura <c-4>8 <b-3>32 <a-1> <b-3> <c-4>]
| 
        }
}

middle = \relative c {
        \fingering
        \override NoteColumn #'ignore-collision = ##t 

        \repeat volta 2 {
                s1 <e-2 g>4 <g b> <b-3 e-4>8. b16\rest <g-0 b-3>8 b\rest | 
        }
}
        
bass = \relative c {
        \fingering
        \override NoteColumn #'ignore-collision = ##t 

        \repeat volta 2 {
                s2.. r8 |
                <e,-1>4 e e e8 a\rest |
        }
}

thescore = \score {
        <<
                \context Staff = guitar {
                        \time 4/4
                        \set Staff.midiInstrument="acoustic guitar (nylon)"
                        \key e \minor
                        \clef "treble_8"
                        \tempo "Adagio assai"
                        \mergeDifferentlyHeadedOn
                        \mergeDifferentlyDottedOn
                        <<
                                \context Voice = "1" { \voiceOne \treble }
                                \context Voice = "2" { \voiceTwo \middle }
                                \context Voice = "4" { \voiceFour \bass }
                        >>
                }
        >>
}

\score {
        \thescore
        \layout {
                \context {
                        \Staff \override KeySignature #'space-alist = 
                                #'((time-signature extra-space . 0)
                                        (staff-bar extra-space . 0)
                                        (right-edge extra-space . 0)
                                        (first-note fixed-space . 4))
                        }
                }
}
%===========================================================================
========

Nick Payne