Too many colliding rests

[Phil Holmes]

With the code at the end of this report, I get pretty good output, but get 
the following in the log file:

Fitting music on 1 page...
Drawing systems...
warning: too many colliding rests
warning: too many colliding rests

The warnings aren't there unless I have the 3rd voice.  Seems like a bug to 
me, and I can't find a report on the tracker?

\relative c'{
\new Staff
<<
 \new Voice { \voiceOne f'8 f f r f r \oneVoice }
 \new Voice { \voiceTwo d,8 d d r d r \oneVoice }
 \new Voice { \voiceFour \tieUp a'2~ a \oneVoice }
> >
}

--
Phil Holmes
Bug Squad