bug: whole note collision

[Bertalan Fodor]

Whole notes are collides with other notes in polyphonic situations.

\version "2.4.2"

\score {
   \new Staff  {
       \relative c'' {
           << { c1 c1 } \\ { c2 c2 b4 b4 b4 b4} >>
       }
   }    
}