automatic note splitting and ties

[Stefan Thomas]

Dear lilypond-users,
I have a problem with ties in connection with automatic note splitting. I don't understand why the ties in the below quoted example look so strange:
Is it a bug?
\score {
    \new Staff {
        \new Voice \with {
  \remove "Note_heads_engraver"
  \consists "Completion_heads_engraver"
  }
  r2
 
  r2 < e  c' >4 < f  des' >8 < des'  ees' >4 -> < c'  e' >
  r8 < e  c' >4 < f  des' >8 < des'  ees' >4 -> < c'  e' > < b  f' > r8 r4
 
   r2 < e  c' >4 < f  des' >8 < des'  ees' >8~ -> < des'  ees' >8 < c'  e' >
  
   } %staff ende
}