Strange Behaviour of same-note polyphonic

[Arjan Bos]

Hi list,

I have found something peculiar in lilypond 2.4.2. I'm setting a piece 
that has, in a few cases, two voices instead of one. Browsing the 
manual, I found the << a \\ b >> syntax. So far, so good.

Normally, when two notes are the same, they are printed overlapping. 
However, when introducing two notes that are the same, and that are 
printed without a stem, they do not overlap. Here's a small example:

\score {
  \new Staff {
    \relative c' {
      r2 r4 r8
      << { fis8( | e) } \\ { fis8( | e)} >>
      r2 r4 r8 |
      r2 r4 r8
      << { fis8( | e4) } \\ { fis8( | e4) } >>
      r2. |
      r2 r4 r8
      << { fis8( | e2) } \\ { fis8( | e2) } >>
      r2 |
      r2 r4 r8
      %% this one goes wrong ?
      << { fis8( | e1) } \\ { fis8( | e1) } >>

    }
  }
}

I'm sure it could be even more concise. Please note that the whole 
notes at the end are not overlapping. How can I make them overlap?

TIA,
Arjan

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