rest collision in tabstaff

[Hernan]

I don't understand why this simple .ly file gives me the warning (a lot ; i copy
here only one measure) which states (twice) :

"warning: can't resolve rest collision: rest direction not set "


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

top = \transpose c c' { <e, b, e g >4 <e, b, e g >4 a8\rest a8
}

bass = \transpose c c { e,4 e,4 c4\rest
}

thescoreTab = \score { << \new Staff    {
 \clef "G_8"  \time 3/4  \key e \minor  <<
         \voiceOne  { \stemUp   \top  }
         \new Voice { \voiceTwo \bass } >>
}       {
        \context TabStaff {      <<
  \context TabVoice { \top  }
  \new     TabVoice { \bass }    >> 
}
} >>
 \layout {}
}
\book { \paper {}
\score { \thescoreTab }
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


The problem seems to be with the tabstaff. (BTW, I'd like to have a way to
suppress rests and beams and ... in tab notation; yes, I know I can make them
transparent, but that doesn't satisfy me: thay might be transparent, but they
are still there; they affect spacings ... and collisions; and the spacing-rods
thing does not seem to help much).

The result (version 2.10.19-1.mingw) can be see here:
http://hjg.com.ar/varios/ej2x.png
Notice that there is no visible collision. Further, I couldnt supress the
warning by moving the rests in the tab (with ExtraOffset), nor by turning them
transparent.

Any help would be appreciated.

Hernan