Problem with \ottava #-1

[Robert Blackstone]

Dear all,

I have been transcribing some piano pieces, with two voices in each staff. 
In the lower staff some of the notes reach down very far, and have many 
auxiliary lines. For easier readability I have made a version with \ottava #-1 
for the lowest notes in the lowest voice, voice 5.
But something strange happened. This \ottava #-1 also changed the  notes of 
voice 4, the upper voice of the lower staff.
I have not been able to reproduce this effect in a ME, which works perfectly, 
as seen in this snippet

%%%%%%%%%%%%%%%%%%%

\version "2.19.81.1" 
PartPFourVoiceOne = {\clef "bass" \key c \minor \time 9/8


        d'8 \rest <bes! es' >8^\markup {the original}( [ as8 ]  g8) [ bes8( f8 
] es4.)| %P4V1-16a
        d8 \rest <bes,! es >8^\markup {the desired simplified}( [ as,8 ]  g,8) 
[ bes,8( f,8 ] es,4.)| %P4V1-16b
}
 PartPFiveVoiceOne = {\clef "bass" \key c \minor \time 9/8
 
         g,,2.~ g,,4.  | %P5V1-16
        \tieDown\stemDown \ottava #-1 g,,2.~ g,,4. \ottava #0 | %P5V1-16
}
\score {
\new Staff = "lower" 
                << 
                \new  Voice = "PartPFourVoiceOne"  \PartPFourVoiceOne 
                \new  Voice = "PartPFiveVoiceOne" \PartPFiveVoiceOne 
                        
                >>
                }

        %This is what I get in the real score (I faked it here) 
                
                PartPFourVoiceOne = {\clef "bass" \key c \minor \time 9/8
        d'8 \rest <bes! es' >8^\markup {this is what I get (faked here)}( [ as8 
]  g8) [ bes8( f8 ] es4.)| %P4V1-16a
        %d8 \rest <bes,! es >8( [ as,8 ]  g,8) [ bes,8( f,8 ] es,4.)| %P4V1-16b
}
 PartPFiveVoiceOne = {\clef "bass" \key c \minor \time 9/8
 
         %g,,2.~ g,,4.  | %P5V1-16
        \tieDown\stemDown \ottava #-1 g,,2.~ g,,4. \ottava #0 | %P5V1-16
}

\score {
\new Staff = "lower" 
                << 
                \new  Voice = "PartPFourVoiceOne"  \PartPFourVoiceOne 
                \new  Voice = "PartPFiveVoiceOne" \PartPFiveVoiceOne 
                        
                >>
                }
                
                %%%%%%%%%%%%%%%%%%%

Does anybody know, or suspect what could be the cause of this aberration?

Thanks in advance for any advice or suggestion.

Best regards, 

Robert Blackstone