Wrong positioning of rests using 2 voices in a staff

[Henri Manson]

Hi there,

I think that maybe I have found a bug in lilypond 2.6.0. I have a score 
with a bass clef and two voices, one has the stems up the other the 
stems down. When I switch the order of the two voices of the original 
file (good.ly) the rests aren't positioned correct anymore (bad.ly). I 
think the other of the voices shouldn't matter. Can you enlighten me?

Kind regards,

Henri Manson

\version "2.6.0"
\new Staff
{
        \clef bass
        \key f \major
        \time 6/8 
        <<
        { \stemDown d2. d d } \\
        { \stemUp a8 r a-. [ a-. ] r a-. a r a-. [ a-. ] r a-. a r a [ a ] r a }
        >>
}

\version "2.6.0"
\new Staff
{
        \clef bass
        \key f \major
        \time 6/8 
        <<
        { \stemUp a8 r a-. [ a-. ] r a-. a r a-. [ a-. ] r a-. a r a [ a ] r a 
} \\
        { \stemDown d2. d d }
        >>
}